[master] fix logic error in TableInfo::UpdateMetrics()

TabletInfo::tablet_map_ is keyed by tablet partition start key,
not tablet UUID.

This is a follow-up to 06a62ec681009b146de3f73808711161c5bed12d.

Change-Id: Ic7d22f4b1fedeb341d261c3ac2e61a29feb3cb2d
Reviewed-on: http://gerrit.cloudera.org:8080/17856
Tested-by: Kudu Jenkins
Reviewed-by: Abhishek Chennaka <achennaka@cloudera.com>
Reviewed-by: Yifan Zhang <chinazhangyifan@163.com>
Reviewed-by: Bankim Bhavsar <bankim@cloudera.com>
1 file changed