Get rid of magic masks in cluster locking code - clvmd part.

Get rid of magic masks in cluster locking code - clvmd part.

- do_command and lock_vg expect flags (no change here)

Bug fixes:
- lock_vg should check for NONBLOCK on lock_cmd, flags have this bit masked-out

- do_pre/post_command expect do not mask flag at all, this causes that
the code inside is never run! (see following patches, these functions
expect plain command without flags)