Clean up wait_for_resource_deletion message

Add missing space and punctuation to make this
message look cleaner.

Change-Id: I595291b68d4fef884888668d3e3c2d5d73b0c4d9
diff --git a/tempest/lib/common/rest_client.py b/tempest/lib/common/rest_client.py
index 3f735f5..ef14dfc 100644
--- a/tempest/lib/common/rest_client.py
+++ b/tempest/lib/common/rest_client.py
@@ -907,8 +907,8 @@
             if int(time.time()) - start_time >= self.build_timeout:
                 message = ('Failed to delete %(resource_type)s %(id)s within '
                            'the required time (%(timeout)s s). Timer started '
-                           'at %(start_time)s. Timer ended at %(end_time)s'
-                           'waited for %(wait_time)s' %
+                           'at %(start_time)s. Timer ended at %(end_time)s. '
+                           'Waited for %(wait_time)s s.' %
                            {'resource_type': self.resource_type, 'id': id,
                             'timeout': self.build_timeout,
                             'start_time': start_time,