tests: Add pseries-phb-user-alias

tests: Add pseries-phb-user-alias

This is the same as the existing pseries-phb-simple, except that
each of the controllers is given a user alias. If we tried to
start the resulting guest, we'd get an error:

  Bus 'ua-phb0' not found

This is because, at the QEMU command line level, the default PHB
is not represented and so it can't be given a custom alias. We're
going to address this issue in a follow-up commit.

Signed-off-by: Andrea Bolognani <abologna@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>