Plugin Test: Add NO_STATE_CHANGE error detection for volume mask and unmask.
Plugin Test: Add NO_STATE_CHANGE error detection for volume mask and unmask.

 * Plugin should raise NO_STATE_CHANGE when volume already masked on
   volume_mask()
 * Plugin should raise NO_STATE_CHANGE when volume is not masked on
   volume_unmask()

Signed-off-by: Gris Ge <e24f3acbe39bf94f92e8af3c48f8852106ad5ad7@redhat.com>

joehandzik/libstoragemgmt,cathay4t/libstoragemgmt,lazy404/libstoragemgmt,libstorage/libstoragemgmt,jumitche/libstoragemgmt,cathay4t/libstoragemgmt,jumitche/libstoragemgmt,cathay4t/libstoragemgmt,tasleson/libstoragemgmt,tasleson/libstoragemgmt,lazy404/libstoragemgmt,cathay4t/libstoragemgmt,jumitche/libstoragemgmt,libstorage/libstoragemgmt,libstorage/libstoragemgmt,libstorage/libstoragemgmt,tasleson/libstoragemgmt,tasleson/libstoragemgmt,libstorage/libstoragemgmt,joehandzik/libstoragemgmt,jumitche/libstoragemgmt,tasleson/libstoragemgmt,joehandzik/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,joehandzik/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,lazy404/libstoragemgmt,lazy404/libstoragemgmt,cathay4t/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt,jumitche/libstoragemgmt,HP-Scale-out-Storage/libstoragemgmt