Invalidate filters  on HSMs before rescanning extended VG

domainMonitor thread might use stale lvm filters while running vgs
command after extending of the VG (added PV is missed in the filter
set). Since LvmCache doesn't invalidate filters, the volume
group  is marked as partial and domainMonitor selftest fails
(host goes to non-operational status). By design filter should be
invalidated if cmd returns nonzero code but vgs returns zero even if
devices are filtered . The patch introduces public  method for
filter invalidation and calls it from the getDevicesVisibility
because getDevicesVisibility is called on all DC hosts after
adding new device but before extendSD.

Change-Id: If1eeed1c203f2c8c73370987048565d665932299
Bugzilla-Url: https://bugzilla.redhat.com/1022976
Signed-off-by: Pavel Zhukov <pzhukov@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/20552
Reviewed-by: Tomáš Došek <tdosek@redhat.com>
Reviewed-by: Sergey Gotliv <sgotliv@redhat.com>
Reviewed-by: Ayal Baron <abaron@redhat.com>
Reviewed-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>