Fix virt-aa-helper when host and os.type arch differ

Fix virt-aa-helper when host and os.type arch differ

* src/security/virt-aa-helper.c: get_definition() now calls the new
  caps_mockup() function which will parse the XML for os.type,
  os.type.arch and then sets the wordsize.  These attributes are needed
  only to get a valid virCapsPtr for virDomainDefParseString(). The -H
  and -b options are now removed from virt-aa-helper (they weren't used
  yet anyway).
* tests/virt-aa-helper-test: extend and fixes tests, chmod'ed 755