Adds Missing _() for Exception Message Translation

Reasons:
- Exception messages missing underscores. This is necessary to
  mark messages as ready for translation, and is already the
  defacto standard across the trove codebase,as per,
  https://wiki.openstack.org/wiki/Translations
- Because of incorrect Exception messages, it does not overrides
  the default message of BadRequest.

Changes:
- Adds the missing underscore function to wrap a few user-facing
  exception messages.

Change-Id: Ib4a183f717146493e514b8169679a57cc2ecfd01
Closes-Bug: #1264688

trove/guestagent/datastore/mysql/service.py

@@ -350,8 +350,10 @@ class MySqlAdmin(object):
         try:
             user.name = username  # Could possibly throw a BadRequest here.
         except exceptions.ValueError as ve:
-            raise exception.BadRequest("Username %s is not valid: %s"
-                                       % (username, ve.message))
+            raise exception.BadRequest(_("Username %(user)s is not valid"
+                                         ": %(reason)s") %
+                                       {'user': username, 'reason': ve.message}
+                                       )
         with LocalSqlClient(get_engine()) as client:
             q = sql_query.Query()
             q.columns = ['User', 'Host', 'Password']

trove/instance/models.py

@@ -560,13 +560,13 @@ class Instance(BuiltInstance):
             self.validate_can_perform_action()
             LOG.info("Resizing volume of instance %s..." % self.id)
             if not self.volume_size:
-                raise exception.BadRequest("Instance %s has no volume."
+                raise exception.BadRequest(_("Instance %s has no volume.")
                                            % self.id)
             old_size = self.volume_size
             if int(new_size) <= old_size:
-                msg = ("The new volume 'size' must be larger than the current "
-                       "volume size of '%s'")
-                raise exception.BadRequest(msg % old_size)
+                raise exception.BadRequest(_("The new volume 'size' must be "
+                                             "larger than the current volume "
+                                             "size of '%s'") % old_size)
             # Set the task to Resizing before sending off to the taskmanager
             self.update_db(task_status=InstanceTasks.RESIZING)
             task_api.API(self.context).resize_volume(new_size, self.id)