There were two different code paths used to get the os_type and
os_version for bare metal machines and vps machines.  This moves
get_distro and get_distro_version back into teuthology.misc and uses
those functions to retrieve os_version and os_type for both bare metal
and vps machines.

When the bare metal machines weren't using get_distro for os_type it
would set os_type to None when there were was not a os_type in the
config or a --os-type flag given.  Now, os_type will be properly
defaulted to ubuntu for bare metal machines.

Signed-off-by: Andrew Schoen <aschoen@redhat.com>