HADOOP-18155. Refactor tests in TestFileUtil (#4053)

[jojochuang]

(cherry picked from commit d0fa9b5)

Conflicts:
hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/FileUtil.java
hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/fs/TestFileUtil.java

Description of PR

How was this patch tested?

For code changes:

• Does the title or this PR starts with the corresponding JIRA issue id (e.g. 'HADOOP-17799. Your PR title ...')?
• Object storage: have the integration tests been executed and the endpoint declared according to the connector-specific documentation?
• If adding new dependencies to the code, are these dependencies licensed in a way that is compatible for inclusion under ASF 2.0?
• If applicable, have you updated the LICENSE, LICENSE-binary, NOTICE-binary files?

[hadoop-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	9m 43s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 0s		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.
			_ branch-3.3 Compile Tests _
+1 💚	mvninstall	33m 39s		branch-3.3 passed
+1 💚	compile	18m 16s		branch-3.3 passed
+1 💚	checkstyle	0m 48s		branch-3.3 passed
+1 💚	mvnsite	1m 31s		branch-3.3 passed
+1 💚	javadoc	1m 34s		branch-3.3 passed
+1 💚	spotbugs	2m 21s		branch-3.3 passed
+1 💚	shadedclient	26m 42s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 56s		the patch passed
+1 💚	compile	17m 16s		the patch passed
+1 💚	javac	17m 16s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	0m 46s		hadoop-common-project/hadoop-common: The patch generated 0 new + 60 unchanged - 15 fixed = 60 total (was 75)
+1 💚	mvnsite	1m 30s		the patch passed
+1 💚	javadoc	1m 31s		the patch passed
+1 💚	spotbugs	2m 32s		the patch passed
+1 💚	shadedclient	26m 46s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	16m 56s		hadoop-common in the patch passed.
+1 💚	asflicense	0m 47s		The patch does not generate ASF License warnings.
		162m 22s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4063/1/artifact/out/Dockerfile
GITHUB PR	#4063
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell
uname	Linux 973e88b52056 4.15.0-162-generic #170-Ubuntu SMP Mon Oct 18 11:38:05 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	branch-3.3 / 2948e6f
Default Java	Private Build-1.8.0_312-8u312-b07-0ubuntu1~18.04-b07
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4063/1/testReport/
Max. process+thread count	1236 (vs. ulimit of 5500)
modules	C: hadoop-common-project/hadoop-common U: hadoop-common-project/hadoop-common
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4063/1/console
versions	git=2.17.1 maven=3.6.0 spotbugs=4.2.2
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[iwasakims]

LGTM.

[GauthamBanasandra]

LGTM