block placement: test DataDirGroups on old servers
block placement: test DataDirGroups on old servers

This patch adds a test ensuring that servers that ran before commit
732ee211a31335a1b146428b15887d1f26468a3a (whose tablet metadata
files do not have DataDirGroupPBs) will create DataDirGroupPBs upon
starting up.

The test creates a tablet, removes the DataDirGroupPB on-disk, and
restarts the server, ensuring a new group is created.

Change-Id: Id27d7a248c129299fb451ce90519fc16c0a105e4
Reviewed-on: http://gerrit.cloudera.org:8080/7088
Tested-by: Kudu Jenkins
Reviewed-by: David Ribeiro Alves <dbbafdb4f25eb0c1ff3facf0e5f2f27705055af1@gmail.com>

andrwng/kudu,helifu/kudu,EvilMcJerkface/kudu,helifu/kudu,InspurUSA/kudu,helifu/kudu,InspurUSA/kudu,cloudera/kudu,andrwng/kudu,helifu/kudu,InspurUSA/kudu,cloudera/kudu,andrwng/kudu,cloudera/kudu,helifu/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,cloudera/kudu,andrwng/kudu,helifu/kudu,EvilMcJerkface/kudu,andrwng/kudu,InspurUSA/kudu,helifu/kudu,EvilMcJerkface/kudu,InspurUSA/kudu,helifu/kudu,andrwng/kudu,EvilMcJerkface/kudu,EvilMcJerkface/kudu,andrwng/kudu,cloudera/kudu,EvilMcJerkface/kudu,cloudera/kudu,cloudera/kudu,InspurUSA/kudu,EvilMcJerkface/kudu,helifu/kudu,andrwng/kudu,cloudera/kudu,andrwng/kudu,InspurUSA/kudu,InspurUSA/kudu,cloudera/kudu