HDFS-16698. Add a metric to sense possible MaxDirectoryItemsExceededException in time.

[ZanderXu]

Description of PR

In our prod environment, we occasionally encounter MaxDirectoryItemsExceededException caused job failure.

org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.hdfs.protocol.FSLimitException$MaxDirectoryItemsExceededException): 
The directory item limit of /user/XXX/.sparkStaging is exceeded: limit=1048576 items=1048576

In order to avoid it, we add a metric to sense possible MaxDirectoryItemsExceededException in time. So that we can process it in time to avoid job failure.

[hadoop-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Logfile	Comment
+0 🆗	reexec	0m 50s		Docker mode activated.
			_ Prechecks _
+1 💚	dupname	0m 0s		No case conflicting files found.
+0 🆗	codespell	0m 1s		codespell was not available.
+0 🆗	detsecrets	0m 1s		detect-secrets 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 _
+0 🆗	mvndep	15m 7s		Maven dependency ordering for branch
+1 💚	mvninstall	26m 21s		trunk passed
+1 💚	compile	6m 40s		trunk passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	compile	6m 10s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	checkstyle	1m 38s		trunk passed
+1 💚	mvnsite	2m 52s		trunk passed
+1 💚	javadoc	2m 25s		trunk passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javadoc	3m 7s		trunk passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	5m 10s		trunk passed
+1 💚	shadedclient	22m 5s		branch has no errors when building and testing our client artifacts.
			_ Patch Compile Tests _
+0 🆗	mvndep	0m 34s		Maven dependency ordering for patch
+1 💚	mvninstall	2m 9s		the patch passed
+1 💚	compile	5m 56s		the patch passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javac	5m 56s		the patch passed
+1 💚	compile	5m 39s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	javac	5m 39s		the patch passed
+1 💚	blanks	0m 0s		The patch has no blanks issues.
-0 ⚠️	checkstyle	1m 18s	/results-checkstyle-hadoop-hdfs-project.txt	hadoop-hdfs-project: The patch generated 1 new + 207 unchanged - 0 fixed = 208 total (was 207)
+1 💚	mvnsite	2m 15s		the patch passed
+1 💚	javadoc	1m 43s		the patch passed with JDK Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1
+1 💚	javadoc	2m 36s		the patch passed with JDK Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
+1 💚	spotbugs	4m 51s		the patch passed
+1 💚	shadedclient	20m 32s		patch has no errors when building and testing our client artifacts.
			_ Other Tests _
+1 💚	unit	238m 21s		hadoop-hdfs in the patch passed.
+1 💚	unit	22m 38s		hadoop-hdfs-rbf in the patch passed.
+1 💚	asflicense	1m 19s		The patch does not generate ASF License warnings.
		405m 25s

Subsystem	Report/Notes
Docker	ClientAPI=1.41 ServerAPI=1.41 base: https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4644/1/artifact/out/Dockerfile
GITHUB PR	#4644
Optional Tests	dupname asflicense compile javac javadoc mvninstall mvnsite unit shadedclient spotbugs checkstyle codespell detsecrets
uname	Linux 3dd0bd8d9cab 4.15.0-112-generic #113-Ubuntu SMP Thu Jul 9 23:41:39 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	dev-support/bin/hadoop.sh
git revision	trunk / a2fef12
Default Java	Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
Multi-JDK versions	/usr/lib/jvm/java-11-openjdk-amd64:Private Build-11.0.15+10-Ubuntu-0ubuntu0.20.04.1 /usr/lib/jvm/java-8-openjdk-amd64:Private Build-1.8.0_312-8u312-b07-0ubuntu1~20.04-b07
Test Results	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4644/1/testReport/
Max. process+thread count	3046 (vs. ulimit of 5500)
modules	C: hadoop-hdfs-project/hadoop-hdfs hadoop-hdfs-project/hadoop-hdfs-rbf U: hadoop-hdfs-project
Console output	https://ci-hadoop.apache.org/job/hadoop-multibranch/job/PR-4644/1/console
versions	git=2.25.1 maven=3.6.3 spotbugs=4.2.2
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