HBASE-21905: [FIFOCompaction] Don't compact already inflight store files

[bharathv]

This one surfaced as a flake test but turns out to be a legit bug
in FIFOCompaction code. FifoCompaction does not check if an empty
store file is already being compacted by an in-flight compaction
request and still enqueues. It can potentially race with a running
compaction (as in this test case, see jira for the exact exception).

Fixes the edge case and cleans up the test code a bit.

[bharathv]

@openinx you added the relevant code and the test, can you please take a look when you get a chance? Thanks.

While the PR is for branch-1, it also applies to other branches. Will forward-port once it is committed.

[Apache-HBase]

💔 -1 overall

Vote	Subsystem	Runtime	Comment
+0 🆗	reexec	1m 32s	Docker mode activated.
		_ Prechecks _
+1 💚	dupname	0m 0s	No case conflicting files found.
+1 💚	hbaseanti	0m 0s	Patch does not have any anti-patterns.
+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.
		_ branch-1 Compile Tests _
+1 💚	mvninstall	10m 14s	branch-1 passed
+1 💚	compile	0m 53s	branch-1 passed with JDK v1.8.0_252
+1 💚	compile	0m 48s	branch-1 passed with JDK v1.7.0_262
+1 💚	checkstyle	1m 53s	branch-1 passed
+1 💚	shadedjars	3m 17s	branch has no errors when building our shaded downstream artifacts.
+1 💚	javadoc	0m 49s	branch-1 passed with JDK v1.8.0_252
+1 💚	javadoc	0m 41s	branch-1 passed with JDK v1.7.0_262
+0 🆗	spotbugs	3m 13s	Used deprecated FindBugs config; considering switching to SpotBugs.
+1 💚	findbugs	3m 9s	branch-1 passed
		_ Patch Compile Tests _
+1 💚	mvninstall	2m 3s	the patch passed
+1 💚	compile	0m 48s	the patch passed with JDK v1.8.0_252
+1 💚	javac	0m 48s	the patch passed
+1 💚	compile	0m 47s	the patch passed with JDK v1.7.0_262
+1 💚	javac	0m 47s	the patch passed
+1 💚	checkstyle	1m 43s	the patch passed
+1 💚	whitespace	0m 0s	The patch has no whitespace issues.
+1 💚	shadedjars	3m 5s	patch has no errors when building our shaded downstream artifacts.
+1 💚	hadoopcheck	5m 2s	Patch does not cause any errors with Hadoop 2.8.5 2.9.2.
+1 💚	javadoc	0m 33s	the patch passed with JDK v1.8.0_252
+1 💚	javadoc	0m 43s	the patch passed with JDK v1.7.0_262
+1 💚	findbugs	3m 5s	the patch passed
		_ Other Tests _
-1 ❌	unit	153m 24s	hbase-server in the patch failed.
+1 💚	asflicense	0m 30s	The patch does not generate ASF License warnings.
		198m 49s

Reason	Tests
Failed junit tests	hadoop.hbase.client.TestAdmin1

Subsystem	Report/Notes
Docker	Client=19.03.11 Server=19.03.11 base: https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1829/1/artifact/out/Dockerfile
GITHUB PR	#1829
JIRA Issue	HBASE-21905
Optional Tests	dupname asflicense javac javadoc unit spotbugs findbugs shadedjars hadoopcheck hbaseanti checkstyle compile
uname	Linux ab1aca1e8c9f 4.15.0-101-generic #102-Ubuntu SMP Mon May 11 10:07:26 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	/home/jenkins/jenkins-slave/workspace/Base-PreCommit-GitHub-PR_PR-1829/out/precommit/personality/provided.sh
git revision	branch-1 / d889c7b
Default Java	1.7.0_262
Multi-JDK versions	/usr/lib/jvm/zulu-8-amd64:1.8.0_252 /usr/lib/jvm/zulu-7-amd64:1.7.0_262
unit	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1829/1/artifact/out/patch-unit-hbase-server.txt
Test Results	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1829/1/testReport/
Max. process+thread count	5038 (vs. ulimit of 10000)
modules	C: hbase-server U: hbase-server
Console output	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1829/1/console
versions	git=1.9.1 maven=3.0.5 findbugs=3.0.1
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[bharathv]

Test failure doesn't seem related to the patch and is occasionally failing with similar symptoms on branch-1 (which is a separate issue)..