There are multiple steps of setting up the domain definition prior to
formatting the command line for the tests. Extract it to a separate
function so that it's self-contained and also will allow re-running the
command line formatting which will be necessary for QMP schema
validation tests.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NEric Blake <eblake@redhat.com>