IMPALA-762: Add the query status to Beeswax::get_log() and pick it up in the Impala shell.

COMPUTE STATS is an async DDL command. When COMPUTE STATS fails it will set the
query status of the QueryExecState properly, but the original Beeswax::query() RPC
won't throw. The Impala shell sometimes did not pick up and display the
query status because no RPC actually threw. To fix this, I modified
Beeswax::get_log() to include the query status if it is not ok. The shell looks
for a special prefix to distinguish the query status from the runtime state error log.

Change-Id: I0d9dbf0801629a37de22ea4ebb6d2e5d53b836ef
Reviewed-on: http://gerrit.ent.cloudera.com:8080/1899
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins