Add detection of mysql restart failure

The present script that is put in place to handle restarts of mysql,
returns an exit code of 0 when a restart has failed as the return
code from start is not captured inside the restart sequence.

This change updates the logic in the script to detect the restart
failure and exit the script with an exit code of 1. If the logic
is already found, the script prints a warning.

Filed with Percona:
https://bugs.launchpad.net/percona-xtradb-cluster/+bug/1339894

Change-Id: Ifdbaa11010cf19ab53c5d2fe4bbec186e58fe6dc
Closes-Bug: 1337344
Merge "Add detection of mysql restart failure"