Don't hardcode strict Fabric version

We need this patch as intermediate step in order to:

* do not break building fuel master iso
* to get new fabric in our mirrors

Related change to fuel-main: I6755b6280f60b86affc8b051ab68bb52204f8810
Related-Bug: #1358265

Change-Id: Icab1b20fbabc49885a49fc9cdf17d6883fcdde28