openSUSE 13.1 was discontinued on Feb 3rd, 2016, so defaulting
to it doesn't make sense (see https://en.opensuse.org/Lifetime).
Leap 42.2 is the most current release that is supported by
disk-image-builder and being tested in a 3rd party ci.
Enable functests for it to ensure we're not regressing again.
Moved to non-voting gate first.
Depends-On: Iff495b3cd0b6c3558c44cf4883651eca67b572d6
Change-Id: Iae6cd34a5853f1e309861c554d94d8595cbd9993
