Fixed some ubuntu points in pmanager.py

Added umounting /dev/sda3 apart from unmounting /target.
Added additional lvm cleaning right after creating
physical volume partitions. If a new physical volume
partition matches the boundaries of the previous one, we can
not reread partition table then. Additional lvm cleaning
allows to avoid this such a kind of undesirable behaviour.

Closes-Bug: #1297792
Change-Id: Ibce615837b7d08806cf7b551d40f8dbc4b03b8b1
Merge "Fixed some ubuntu points in pmanager.py"