HADOOP-17062. Fix shelldocs path in Jenkinsfile

[aajisaka]

JIRA: https://issues.apache.org/jira/browse/HADOOP-17062

If this PR is merged. I'll update the config in the PreCommit-(HADOOP|HDFS|MAPREDUCE|YARN)-Build Jenkins jobs.

[aajisaka]

Looks good https://builds.apache.org/job/hadoop-multibranch/job/PR-2049/1/console

15:49:29  ============================================================================
15:49:29  ============================================================================
15:49:29                            shelldocs plugin: trunk
15:49:29  ============================================================================
15:49:29  ============================================================================
15:49:29  
15:49:29  
15:49:29  Running shelldocs against all identifiable shell scripts

[hadoop-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Comment
+0 🆗	reexec	1m 30s	Docker mode activated.
		_ Prechecks _
+1 💚	dupname	0m 0s	No case conflicting files found.
+1 💚	@author	0m 0s	The patch does not contain any @author tags.
		_ trunk Compile Tests _
+1 💚	shadedclient	16m 21s	branch has no errors when building and testing our client artifacts.
		_ Patch Compile Tests _
+1 💚	shellcheck	0m 0s	There were no new shellcheck issues.
+1 💚	shelldocs	0m 15s	There were no new shelldocs issues.
+1 💚	whitespace	0m 0s	The patch has no whitespace issues.
+1 💚	shadedclient	16m 2s	patch has no errors when building and testing our client artifacts.
		_ Other Tests _
+1 💚	asflicense	0m 31s	The patch does not generate ASF License warnings.
		36m 21s

Subsystem	Report/Notes
Docker	ClientAPI=1.40 ServerAPI=1.40 base: https://builds.apache.org/job/hadoop-multibranch/job/PR-2049/1/artifact/out/Dockerfile
GITHUB PR	#2049
Optional Tests	dupname asflicense shellcheck shelldocs
uname	Linux c7de8b8e5e7c 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	personality/hadoop.sh
git revision	trunk / 6288e15
Max. process+thread count	308 (vs. ulimit of 5500)
modules	C: . U: .
Console output	https://builds.apache.org/job/hadoop-multibranch/job/PR-2049/1/console
versions	git=2.17.1 maven=3.6.0 shellcheck=0.4.6
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[iwasakims]

+1.

[ayushtkn]

LGTM

[aajisaka]

Thank you, @iwasakims and @ayushtkn

[aajisaka]

If this PR is merged. I'll update the config in the PreCommit-(HADOOP|HDFS|MAPREDUCE|YARN)-Build Jenkins jobs.

Done. Also updated the config of https://ci-hadoop.apache.org/job/hadoop-qbt-trunk-java8-linux-x86_64/