HADOOP-18009. Reset UserGroupInformation after tests run

[odrepa]

Description of PR

This pull request aims to reset shared state between TestSecureRegistry and TestRegistryOperationUtils, where TestRegistryOperationUtils (namely testUsernameExtractionEnvVarOverrride) fails when run afterwards in the same JVM. While currently test classes are run in separate JVMs, they can be run faster when run in the same JVM, and the shared state can be reset with the proposed patch in this pull request.

How was this patch tested?

Before this patch, if the two test classes TestSecureRegistry and TestRegistryOperationUtils are run in this order within the same JVM (Surefire configuration reuseForks=true), TestRegistryOperationUtils fails. After the patch, the test passes in the order.

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	1m 4s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 2s		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.
			_ trunk Compile Tests _
+1 💚	mvninstall	34m 59s		trunk passed
+1 💚	compile	23m 35s		trunk passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 💚	compile	20m 3s		trunk passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+1 💚	checkstyle	0m 33s		trunk passed
+1 💚	mvnsite	0m 36s		trunk passed
+1 💚	javadoc	0m 35s		trunk passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 💚	javadoc	0m 33s		trunk passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+1 💚	spotbugs	0m 53s		trunk passed
+1 💚	shadedclient	23m 19s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 21s		the patch passed
+1 💚	compile	22m 48s		the patch passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 💚	javac	22m 48s		the patch passed
+1 💚	compile	19m 56s		the patch passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+1 💚	javac	19m 56s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	checkstyle	0m 28s		the patch passed
+1 💚	mvnsite	0m 34s		the patch passed
+1 💚	javadoc	0m 34s		the patch passed with JDK Ubuntu-11.0.11+9-Ubuntu-0ubuntu2.20.04
+1 💚	javadoc	0m 32s		the patch passed with JDK Private Build-1.8.0_292-8u292-b10-0ubuntu1~20.04-b10
+1 💚	spotbugs	1m 0s		the patch passed
+1 💚	shadedclient	23m 8s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	1m 16s		hadoop-registry in the patch passed.
+1 💚	asflicense	0m 50s		The patch does not generate ASF License warnings.
		180m 39s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-3656/1/artifact/out/Dockerfile
GITHUB PR	#3656
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell
uname	Linux 0ab18b58a42f 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	trunk / 7078ebe
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-3656/1/testReport/
Max. process+thread count	524 (vs. ulimit of 5500)
modules	C: hadoop-common-project/hadoop-registry U: hadoop-common-project/hadoop-registry
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-3656/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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