Ubuntu: using 3.11 kernel for MOS versions < 6.0

* Added 'if' condition into ubuntu preseed so as to
  install 3.11 kernel if fuel_version is not equal to 6.0
  trusty kernel if it is.

Change-Id: I495b1da9d4ed5effcaea32b27cd0cc0b5f527075
Related-bug: 1390044
Related-bug: 1383641
Related-bug: 1348331
Merge "Ubuntu: using 3.11 kernel for MOS versions < 6.0"