Extend LVM brick functionality

This patch adds some new methods to the LVM brick:

- VG activation
- VG deactivation
- VG removal
- PV resizing
- Thinpool extension

These changes were initially proposed in
https://review.openstack.org/#/c/110236/ but reworked into a separate
patch-set.

Change-Id: I9070eb5557b5a0ccc0563785f22e5fff7ad332f8