YARN-10054. Upgrade yarn to 1.21.1 in Dockerfile.

[aajisaka]

JIRA: https://issues.apache.org/jira/browse/YARN-10054

[hadoop-yetus]

(!) A patch to the testing environment has been detected.
Re-executing against the patched versions to perform further tests.
The console is at https://builds.apache.org/job/hadoop-multibranch/job/PR-1777/1/console in case of problems.

[hadoop-yetus]

🎊 +1 overall

Vote	Subsystem	Runtime	Comment
+0 🆗	reexec	2m 11s	Docker mode activated.
		_ Prechecks _
+1 💚	dupname	0m 0s	No case conflicting files found.
+0 🆗	shelldocs	0m 0s	Shelldocs was not available.
+1 💚	@author	0m 0s	The patch does not contain any @author tags.
		_ trunk Compile Tests _
+0 🆗	mvndep	1m 22s	Maven dependency ordering for branch
+1 💚	shadedclient	15m 23s	branch has no errors when building and testing our client artifacts.
		_ Patch Compile Tests _
+0 🆗	mvndep	0m 29s	Maven dependency ordering for patch
+1 💚	hadolint	0m 3s	There were no new hadolint issues.
+1 💚	shellcheck	0m 0s	There were no new shellcheck issues.
+1 💚	whitespace	0m 0s	The patch has no whitespace issues.
+1 💚	shadedclient	14m 57s	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 44s

Subsystem	Report/Notes
Docker	Client=19.03.5 Server=19.03.5 base: https://builds.apache.org/job/hadoop-multibranch/job/PR-1777/1/artifact/out/Dockerfile
GITHUB PR	#1777
Optional Tests	dupname asflicense hadolint shellcheck shelldocs
uname	Linux d8ada807e655 4.15.0-70-generic #79-Ubuntu SMP Tue Nov 12 10:36:11 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux
Build tool	maven
Personality	personality/hadoop.sh
git revision	trunk / bc825b9
Max. process+thread count	297 (vs. ulimit of 5500)
modules	C: U:
Console output	https://builds.apache.org/job/hadoop-multibranch/job/PR-1777/1/console
versions	git=2.7.4 maven=3.3.9 shellcheck=0.3.7 hadolint=1.11.1-0-g0e692dd
Powered by	Apache Yetus 0.11.1 https://yetus.apache.org

This message was automatically generated.

[iwasakims]

+1

[aajisaka]

Thank you, @iwasakims