IMPALA-1162: Add GetExecSummary() and GetRuntimeProfile() to HS2

This patch adds RPCs for GetExecSummary() and GetRuntimeProfile() to the
Impala HS2 service, to get reporting parity with the Beeswax service
implementation.

Change-Id: I966a85854e5a657a26c226cc0e68e053fb2aa6c2
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/3902
Reviewed-by: Alex Behm <alex.behm@cloudera.com>
Tested-by: jenkins
Reviewed-on: http://gerrit.sjc.cloudera.com:8080/3944
Reviewed-by: Henry Robinson <henry@cloudera.com>