Run the install_default_update test on UEFI as well
Obviously an installer image may work fine for a BIOS install
but fail for a UEFI install, so we should test it both ways.
This requires the invention of a new (terribly named, but I
couldn't think of anything better...) variable to allow us to
use the 'run test on machine A after test run on machine B'
mechanism without just hardcoding '64bit' as the machine name
in the START_AFTER setting (which would break if we ever wanted
to run update tests on any *other* arch).
Signed-off-by: Adam Williamson <awilliam@redhat.com>