Improve error msg of wait_for_server_status waiter

Previously the error message in case of a timeout was specific
to server boot operation, however, the waiter is used in other
tests, such as resize and unshelve.
The commit modifies the message to be more general.

Change-Id: Ie95362efa9ea295ab13903945fa5f7e573c69ecd
diff --git a/tempest/common/waiters.py b/tempest/common/waiters.py
index c5da412..d88bc05 100644
--- a/tempest/common/waiters.py
+++ b/tempest/common/waiters.py
@@ -77,7 +77,8 @@
             if 'fault' in body:
                 details += 'Fault: %s.' % body['fault']
             if request_id:
-                details += ' Server boot request ID: %s.' % request_id
+                details += ' Request ID of server operation performed before'
+                details += ' checking the server status %s.' % request_id
             raise exceptions.BuildErrorException(details, server_id=server_id)
 
         timed_out = int(time.time()) - start_time >= timeout
@@ -92,7 +93,8 @@
                         'expected_task_state': expected_task_state,
                         'timeout': timeout})
             if request_id:
-                message += ' Server boot request ID: %s.' % request_id
+                message += ' Request ID of server operation performed before'
+                message += ' checking the server status %s.' % request_id
             message += ' Current status: %s.' % server_status
             message += ' Current task state: %s.' % task_state
             caller = test_utils.find_test_caller()