Allow mapping _ to lazy gettext path

Since nova has switched from using gettext.install for
importing the _ function to explicitly importing the _
function from gettextutils, we need to be able to enable
our deferred translation code path on the gettextutils._
function.

Change-Id: I7fec00810ea57c985e1f43c644913a9980b35655
Merge "Allow mapping _ to lazy gettext path"