HDFS-16125: fix the iterator for PartitionedGSet

[xinglin]

fixed the issue that iterator will visit the first partition twice.

also fixed a typo in readTopdUnlock and removed the unused rootDir Inode in PartitionedGSet constructor.

added TestPartitionedGSet.java.

mvn test -Dtest=TestPartitionedGSet passed.

[shvachko]

General note:
Let's not force rebase on every commit.
It really helps to keep the history of changes on a PR.
The final merge to the repo should squash all these commits on the PR and make it one.

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	22m 32s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+1 💚	@author	0m 0s		The patch does not contain any @author tags.
+1 💚	test4tests	0m 0s		The patch appears to include 1 new or modified test files.
			_ fgl Compile Tests _
+0 🆗	mvndep	3m 30s		Maven dependency ordering for branch
-1 ❌	mvninstall	0m 43s	/branch-mvninstall-root.txt	root in fgl failed.
-1 ❌	compile	0m 21s	/branch-compile-root-jdkUbuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.txt	root in fgl failed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.
-1 ❌	compile	0m 21s	/branch-compile-root-jdkPrivateBuild-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.txt	root in fgl failed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.
-0 ⚠️	checkstyle	0m 20s	/buildtool-branch-checkstyle-root.txt	The patch fails to run checkstyle in root
-1 ❌	mvnsite	1m 20s	/branch-mvnsite-hadoop-common-project_hadoop-common.txt	hadoop-common in fgl failed.
-1 ❌	mvnsite	0m 42s	/branch-mvnsite-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in fgl failed.
-1 ❌	javadoc	0m 19s	/branch-javadoc-hadoop-common-project_hadoop-common-jdkUbuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.txt	hadoop-common in fgl failed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.
-1 ❌	javadoc	0m 15s	/branch-javadoc-hadoop-hdfs-project_hadoop-hdfs-jdkUbuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.txt	hadoop-hdfs in fgl failed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.
-1 ❌	javadoc	0m 15s	/branch-javadoc-hadoop-common-project_hadoop-common-jdkPrivateBuild-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.txt	hadoop-common in fgl failed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.
-1 ❌	javadoc	0m 14s	/branch-javadoc-hadoop-hdfs-project_hadoop-hdfs-jdkPrivateBuild-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.txt	hadoop-hdfs in fgl failed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.
-1 ❌	spotbugs	0m 12s	/branch-spotbugs-hadoop-common-project_hadoop-common.txt	hadoop-common in fgl failed.
-1 ❌	spotbugs	0m 11s	/branch-spotbugs-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in fgl failed.
-1 ❌	shadedclient	4m 15s		branch has errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+0 🆗	mvndep	0m 15s		Maven dependency ordering for patch
-1 ❌	mvninstall	0m 11s	/patch-mvninstall-hadoop-common-project_hadoop-common.txt	hadoop-common in the patch failed.
-1 ❌	mvninstall	0m 12s	/patch-mvninstall-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch failed.
-1 ❌	compile	0m 19s	/patch-compile-root-jdkUbuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.txt	root in the patch failed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.
-1 ❌	javac	0m 19s	/patch-compile-root-jdkUbuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.txt	root in the patch failed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.
-1 ❌	compile	0m 16s	/patch-compile-root-jdkPrivateBuild-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.txt	root in the patch failed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.
-1 ❌	javac	0m 16s	/patch-compile-root-jdkPrivateBuild-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.txt	root in the patch failed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.
-1 ❌	blanks	0m 0s	/blanks-eol.txt	The patch has 1 line(s) that end in blanks. Use git apply --whitespace=fix <<patch_file>>. Refer https://git-scm.com/docs/git-apply
-0 ⚠️	checkstyle	0m 18s	/buildtool-patch-checkstyle-root.txt	The patch fails to run checkstyle in root
-1 ❌	mvnsite	0m 13s	/patch-mvnsite-hadoop-common-project_hadoop-common.txt	hadoop-common in the patch failed.
-1 ❌	mvnsite	0m 12s	/patch-mvnsite-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch failed.
-1 ❌	javadoc	0m 16s	/patch-javadoc-hadoop-common-project_hadoop-common-jdkUbuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.txt	hadoop-common in the patch failed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.
-1 ❌	javadoc	0m 13s	/patch-javadoc-hadoop-hdfs-project_hadoop-hdfs-jdkUbuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.txt	hadoop-hdfs in the patch failed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04.
-1 ❌	javadoc	0m 13s	/patch-javadoc-hadoop-common-project_hadoop-common-jdkPrivateBuild-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.txt	hadoop-common in the patch failed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.
-1 ❌	javadoc	0m 13s	/patch-javadoc-hadoop-hdfs-project_hadoop-hdfs-jdkPrivateBuild-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.txt	hadoop-hdfs in the patch failed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10.
-1 ❌	spotbugs	0m 13s	/patch-spotbugs-hadoop-common-project_hadoop-common.txt	hadoop-common in the patch failed.
-1 ❌	spotbugs	0m 13s	/patch-spotbugs-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch failed.
-1 ❌	shadedclient	3m 45s		patch has errors when building and testing our client artifacts.
			_ Other Tests _
-1 ❌	unit	0m 12s	/patch-unit-hadoop-common-project_hadoop-common.txt	hadoop-common in the patch failed.
-1 ❌	unit	0m 13s	/patch-unit-hadoop-hdfs-project_hadoop-hdfs.txt	hadoop-hdfs in the patch failed.
+1 💚	asflicense	0m 31s		The patch does not generate ASF License warnings.
		38m 53s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-3197/4/artifact/out/Dockerfile
GITHUB PR	#3197
JIRA Issue	HDFS-16125
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell
uname	Linux de38ac157114 4.15.0-142-generic #146-Ubuntu SMP Tue Apr 13 01:11:19 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	fgl / 82330f5
Default Java	Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-3197/4/testReport/
Max. process+thread count	84 (vs. ulimit of 5500)
modules	C: hadoop-common-project/hadoop-common hadoop-hdfs-project/hadoop-hdfs U: .
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-3197/4/console
versions	git=2.25.1 maven=3.6.3
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