ceph-volume: remove PVolumes from api/lvm.py

ceph-volume: remove PVolumes from api/lvm.py

And method get_pv() since it's based on PVolumes and get_first_pv() and
get_pvs() can be easily used instead in future. Also, update tests
accordingly.

Signed-off-by: Rishabh Dave <ridave@redhat.com>
(cherry picked from commit 009e9dcebf6e13b6fb66bc0368c907d0b988d127)

 Conflicts:
	src/ceph-volume/ceph_volume/tests/util/test_device.py
	The dummy device path in tests "test_is_lvm_memeber",
	"test_is_not_lvm_memeber" and "test_is_partition" are slightly
	different from master.