fix: semver sorting for kernel packages

[barabo]

The current Debian installer does not sort kernel version numbers using semver, so when the headers version jumped from 96 to 105 - the wrong version is selected.

This change creates a comparator that respects both ABI and kernel version numbers numerically.

[barabo]

See #53

[barabo]

You might also consider letting apt decide which kernel versions to use with something like:

self.run("apt-get install -y make gcc linux-image-cloud-amd64 "
         "linux-headers-cloud-amd64 pciutils gcc make dkms cmake git")

I'm assuming there's a good reason for parsing version numbers explicitly, but it might be better to let apt do this.