Linux Mint support

This patch allows DevStack installation on Linux Mint. Installations
on Linux Mint previously failed since its distribution ID did not
match any of the package installation methods and defaulted to using
rpm packages. Linux Mint is a Ubuntu derivative and such does not have
native support for rpm packages.

This change adds "LinuxMint" to the distribution matching options along
with Debian and Ubuntu.

Change-Id: Ice6a201cabe07373a9c1354699777835addeac53
Fixes: bug #1166422
Merge "Linux Mint support"