Exercise the ABI stability check code in test suite

Exercise the ABI stability check code in test suite

Any test suite which involves a virDomainDefPtr should
call virDomainDefCheckABIStability with itself just as
a basic sanity check that the identity-comparison always
succeeds. This would have caught the recent NULL pointer
access crash.

Make sure we cope with def->name being NULL since the
VMWare config parser produces NULL names.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>