Add rdd function for snapshot read

[mini666]

I added RDD function to HBaseContext.
It is much better to read and access HDFS directly than to read through RegionServer.
This is a method that does not burden HBase.

Working in a single cluster is OK, but HBase 2.1.4 or later is required for working with multiple clusters.
Ref: HBASE-18484 VerifyRep by snapshot does not work when Yarn/SourceHBase…

[asf-ci]

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[asf-ci]

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[HorizonNet]

@mini666 Is there a related Jira ticket for this PR?

[Apache-HBase]

🎊 +1 overall

Vote	Subsystem	Runtime	Comment
+0 🆗	reexec	0m 31s	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.
-0 ⚠️	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.
		_ master Compile Tests _
+1 💚	mvninstall	2m 8s	master passed
+1 💚	compile	1m 8s	master passed
+1 💚	scaladoc	0m 32s	master passed
		_ Patch Compile Tests _
+1 💚	mvninstall	1m 22s	the patch passed
+1 💚	compile	1m 6s	the patch passed
+1 💚	scalac	1m 6s	the patch passed
+1 💚	whitespace	0m 0s	The patch has no whitespace issues.
+1 💚	scaladoc	0m 30s	the patch passed
		_ Other Tests _
+1 💚	unit	5m 46s	hbase-spark in the patch passed.
		13m 21s

Subsystem	Report/Notes
Docker	ClientAPI=1.40 ServerAPI=1.40 base: https://ci-hadoop.apache.org/job/HBase/job/HBase-Connectors-PreCommit/job/PR-40/1/artifact/yetus-precommit-check/output/Dockerfile
GITHUB PR	#40
Optional Tests	dupname scalac scaladoc unit compile
uname	Linux 66f0ad2abba5 4.15.0-60-generic #67-Ubuntu SMP Thu Aug 22 16:55:30 UTC 2019 x86_64 GNU/Linux
Build tool	hb_maven
Personality	dev-support/jenkins/hbase-personality.sh
git revision	master / d3175ad
Test Results	https://ci-hadoop.apache.org/job/HBase/job/HBase-Connectors-PreCommit/job/PR-40/1/testReport/
Max. process+thread count	989 (vs. ulimit of 12500)
modules	C: spark/hbase-spark U: spark/hbase-spark
Console output	https://ci-hadoop.apache.org/job/HBase/job/HBase-Connectors-PreCommit/job/PR-40/1/console
versions	git=2.20.1
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[meszibalu]

@mini666 are you planning to create a Jira ticket for this change?

[Apache-HBase]

💔 -1 overall

Vote	Subsystem	Runtime	Comment
+0 🆗	reexec	0m 0s	Docker mode activated.
-1 ❌	patch	0m 2s	#40 does not apply to master. Rebase required? Wrong Branch? See https://yetus.apache.org/documentation/in-progress/precommit-patchnames for help.

Subsystem	Report/Notes
GITHUB PR	#40
Console output	https://ci-hadoop.apache.org/job/HBase/job/HBase-Connectors-PreCommit/job/PR-40/1/console
versions	git=2.17.1
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[ericsun95]

This is a very nice feature. Do we have any tests though?