Enable LVM snap autoextend

Enable LVM snap autoextend for Cinder.  This is a stopgap
since snapshots fill up while being wiped during volume clone
operations.  (And may at other times as well.)

This is Grizzly backport

Change-Id: I11c58850502f9cb563501d931b8505900e26520e
Made token_format configurable

Fixes: rhbz#975153
Change-Id: Ia679324307d4091f8b8ca98b02ab81760d2b4f8a
Merge "Enable LVM snap autoextend" into grizzly