Makefile.am: ignore false positive pyflakes lvm.py

Temporary workaround.

Change-Id: Id8cdeb0c28c1ee5dc3a18a7688ae60fe641f9a6c
Signed-off-by: Zhou Zheng Sheng <zhshzhou@linux.vnet.ibm.com>
Signed-off-by: Douglas Schilling Landgraf <dougsland@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/12700
Reviewed-by: Dan Kenigsberg <danken@redhat.com>