gitlab: rename the cross build jobs

gitlab: rename the cross build jobs

The pipeline UI will truncate the names of jobs after about 15
characters. As a result with the cross-builds, we truncate the
most important part of the job name. Putting the most important
part first is robust against truncation, and we can drop the
redundant "-cross" stub.

Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Erik Skultety <skultety.erik@gmail.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>