Add the ability to ensure supported kernel

Ubuntu has [deprecated](https://wiki.ubuntu.com/1204_HWE_EOL) all
hardware enablement (HWE) kernels which are basically the kernels for
newer releases backported to this release. They are named with suffixes
of _lts-quantal_, _lts-raring_, _lts_saucy_ and those kernels are only
supported until 14.04.1 is released (Aug 8, 2014)
Merge pull request #204 from alphagov/ensure-hwe-support

Add the ability to ensure supported kernel