Fix openSUSE detection

TRIPLEO_OS_DISTRO needs to be opensuse for openSUSE.
Also, switch to the cross-distro standard way of
detecting distro flavor via /etc/os-release. The old
path is going to be removed soon.

Change-Id: I118ae7bb73f65e60d8313ab8d84eee379ae587eb
Merge "Fix openSUSE detection"