CDH-19292: Impala query on an HBase table takes almost same time as Hive

This commit fixes issue CDH-19292, where querying an HBase table takes
a significant amount of time if HBase has a large (>1K) number of
tables. The performance bottleneck is the call to HBase to retrieve the
table's metadata (column families) during the computation of row stats.
To resolve this issue we cache the column families in the catalog object
associated with an HBase table, so the expensive call to HBase only
happens the first time the table is queried. Subsequent calls use the
cached data.

Change-Id: I0203fee3e73d2a4304530fe0a1ba2cf163f39350
Reviewed-on: http://gerrit.ent.cloudera.com:8080/2672
Reviewed-by: Dimitris Tsirogiannis <dtsirogiannis@cloudera.com>
Reviewed-by: Lenni Kuff <lskuff@cloudera.com>
Tested-by: jenkins