[mb2] Do the best we can with ssu to see if registration is needed

Signed-off-by: David Greaves <david.greaves@jollamobile.com>
[mb2] rpmbuild runs script under -e so 'false' is a problem. Pass args to raw q/make

Signed-off-by: David Greaves <david.greaves@jollamobile.com>
[mb2] only verify_target_dependencies if there is a spec

Signed-off-by: David Greaves <david.greaves@jollamobile.com>
[mb2] Now a spec is optional it's not an error if one is missing in some situations - but equally, we should still look for one and use it if found.

Signed-off-by: David Greaves <david.greaves@jollamobile.com>