HDFS-15935. Use memcpy for copying non-null terminated string.

[GauthamBanasandra]

• strncpy reports a warning if the
  destination string isn't null
  terminated. Since we append a
  custom character at the end ourselves,
  the warning reported by stnrcpy is
  valid, but not relevant.
• Thus, we use memcpy to avoid this
  warning.

[hadoop-yetus]

💔 -1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 32s		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 doesn't appear to include any new or modified tests. Please justify why no new tests are needed for this patch. Also please list what manual steps were performed to verify this patch.
			_ trunk Compile Tests _
+1 💚	mvninstall	33m 25s		trunk passed
+1 💚	compile	2m 47s		trunk passed with JDK Ubuntu-11.0.10+9-Ubuntu-0ubuntu1.20.04
+1 💚	compile	2m 47s		trunk passed with JDK Private Build-1.8.0_282-8u282-b08-0ubuntu1~20.04-b08
+1 💚	mvnsite	0m 29s		trunk passed
+1 💚	shadedclient	53m 29s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+1 💚	mvninstall	0m 16s		the patch passed
+1 💚	compile	2m 34s		the patch passed with JDK Ubuntu-11.0.10+9-Ubuntu-0ubuntu1.20.04
+1 💚	cc	2m 34s		hadoop-hdfs-project_hadoop-hdfs-native-client-jdkUbuntu-11.0.10+9-Ubuntu-0ubuntu1.20.04 with JDK Ubuntu-11.0.10+9-Ubuntu-0ubuntu1.20.04 generated 0 new + 52 unchanged - 8 fixed = 52 total (was 60)
+1 💚	golang	2m 34s		the patch passed
+1 💚	javac	2m 34s		the patch passed
+1 💚	compile	2m 35s		the patch passed with JDK Private Build-1.8.0_282-8u282-b08-0ubuntu1~20.04-b08
+1 💚	cc	2m 35s		hadoop-hdfs-project_hadoop-hdfs-native-client-jdkPrivateBuild-1.8.0_282-8u282-b08-0ubuntu120.04-b08 with JDK Private Build-1.8.0_282-8u282-b08-0ubuntu120.04-b08 generated 0 new + 52 unchanged - 8 fixed = 52 total (was 60)
+1 💚	golang	2m 35s		the patch passed
+1 💚	javac	2m 35s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
+1 💚	mvnsite	0m 17s		the patch passed
+1 💚	shadedclient	13m 37s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	41m 44s		hadoop-hdfs-native-client in the patch passed.
+1 💚	asflicense	0m 34s		The patch does not generate ASF License warnings.
		117m 53s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-2827/1/artifact/out/Dockerfile
GITHUB PR	#2827
Optional Tests	dupname asflicense compile cc mvnsite javac unit codespell golang
uname	Linux f525e1fcc389 4.15.0-136-generic #140-Ubuntu SMP Thu Jan 28 05:20:47 UTC 2021 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / 350ea2f
Default Java	Private Build-1.8.0_282-8u282-b08-0ubuntu1~20.04-b08
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Ubuntu-11.0.10+9-Ubuntu-0ubuntu1.20.04 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_282-8u282-b08-0ubuntu1~20.04-b08
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-2827/1/testReport/
Max. process+thread count	717 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs-native-client U: hadoop-hdfs-project/hadoop-hdfs-native-client
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-2827/1/console
versions	git=2.25.1 maven=3.6.3
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[GauthamBanasandra]

This PR fixes some warnings reported as part of #2792 in CI run #2792 (comment)