CBQE-6184: [1/n] Merge success message check

Scan for a success message in all of the output as opposed to scanning
just the first message which is currently a warning that the progress
bar is disabled.

Change-Id: Ic69cce4a7d2c630552cc3ea2698a95860849c6bb
Reviewed-on: http://review.couchbase.org/c/testrunner/+/139664
Reviewed-by: James Lee <james.lee@couchbase.com>
Tested-by: Asad Zaidi <asad.zaidi@couchbase.com>

pytests/ent_backup_restore/enterprise_backup_restore_base.py

@@ -1475,7 +1475,7 @@ def backup_merge(self):
         remote_client.log_command_output(output, error)
         if error:
             return False, error, "Merging backup failed"
-        elif output and "Merge completed successfully" not in output[0]:
+        elif output and not self._check_output(["succeeded", "successfully"], output):
             return False, output, "Merging backup failed"
         elif not output:
             self.log.info("process cbbackupmge may be killed")