Add sorting for releases collection

  Implement sorting for ReleaseCollection in /api/releases
  Sorting criteria:
  1) Fuel version
  2) OpenStack release
  3) Operating system. Ubuntu is preferred

Change-Id: I6677f449b4435aa57c7e4f1c89a292284014d61c
Closes-Bug: 1377920
Merge "Add sorting for releases collection"