HBASE-23281: Track meta region locations in masters (#830)

[bharathv]

This patch adds a simple cache that tracks the meta region replica
locations. It keeps an eye on the region movements so that the
cached locations are not stale.

This information is used for servicing client RPCs for connections
that use master based registry (HBASE-18095). The RPC end points
will be added in a separate patch.

[Apache-HBase]

🎊 +1 overall

Vote	Subsystem	Runtime	Comment
+0 🆗	reexec	1m 18s	Docker mode activated.
		_ Prechecks _
+1 💚	dupname	0m 0s	No case conflicting files found.
+1 💚	hbaseanti	0m 0s	Patch does not have any anti-patterns.
+1 💚	@author	0m 0s	The patch does not contain any @author tags.
+1 💚	test4tests	0m 0s	The patch appears to include 18 new or modified test files.
		_ branch-2 Compile Tests _
+0 🆗	mvndep	0m 18s	Maven dependency ordering for branch
+1 💚	mvninstall	6m 58s	branch-2 passed
+1 💚	compile	1m 56s	branch-2 passed
+1 💚	checkstyle	2m 28s	branch-2 passed
+1 💚	shadedjars	4m 53s	branch has no errors when building our shaded downstream artifacts.
+1 💚	javadoc	1m 20s	branch-2 passed
+0 🆗	spotbugs	0m 44s	Used deprecated FindBugs config; considering switching to SpotBugs.
+1 💚	findbugs	6m 30s	branch-2 passed
		_ Patch Compile Tests _
+0 🆗	mvndep	0m 16s	Maven dependency ordering for patch
+1 💚	mvninstall	6m 32s	the patch passed
+1 💚	compile	1m 57s	the patch passed
+1 💚	javac	1m 57s	the patch passed
+1 💚	checkstyle	0m 42s	The patch passed checkstyle in hbase-client
+1 💚	checkstyle	0m 14s	The patch passed checkstyle in hbase-zookeeper
+1 💚	checkstyle	1m 25s	hbase-server: The patch generated 0 new + 114 unchanged - 6 fixed = 114 total (was 120)
+1 💚	whitespace	0m 0s	The patch has no whitespace issues.
+1 💚	shadedjars	5m 36s	patch has no errors when building our shaded downstream artifacts.
+1 💚	hadoopcheck	20m 30s	Patch does not cause any errors with Hadoop 2.8.5 2.9.2 or 3.1.2.
+1 💚	javadoc	1m 28s	the patch passed
+1 💚	findbugs	6m 26s	the patch passed
		_ Other Tests _
+1 💚	unit	4m 4s	hbase-client in the patch passed.
+1 💚	unit	0m 54s	hbase-zookeeper in the patch passed.
+1 💚	unit	167m 33s	hbase-server in the patch passed.
+1 💚	asflicense	1m 37s	The patch does not generate ASF License warnings.
		253m 46s

Subsystem	Report/Notes
Docker	Client=19.03.5 Server=19.03.5 base: https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1097/1/artifact/out/Dockerfile
GITHUB PR	#1097
JIRA Issue	HBASE-23281
Optional Tests	dupname asflicense javac javadoc unit spotbugs findbugs shadedjars hadoopcheck hbaseanti checkstyle compile
uname	Linux 893a96afaca9 4.15.0-65-generic #74-Ubuntu SMP Tue Sep 17 17:06:04 UTC 2019 x86_64 GNU/Linux
Build tool	maven
Personality	/home/jenkins/jenkins-slave/workspace/Base-PreCommit-GitHub-PR_PR-1097/out/precommit/personality/provided.sh
git revision	branch-2 / e0f9133
Default Java	1.8.0_181
Test Results	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1097/1/testReport/
Max. process+thread count	4812 (vs. ulimit of 10000)
modules	C: hbase-client hbase-zookeeper hbase-server U: .
Console output	https://builds.apache.org/job/HBase-PreCommit-GitHub-PR/job/PR-1097/1/console
versions	git=2.11.0 maven=2018-06-17T18:33:14Z) findbugs=3.1.11
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[apurtell]

I approved this but seems some of the delta in this one I just reviewed on another PR. Might have a merge conflict.

[bharathv]

Will be merged as a part of #1098