lvm: Do not use udev cache for obtaining device list

lvm is obtaining the device list from udev. When using concurrently,
udev sometimes returns incomplete list, which cause lvm to think that a
vg is missing, and the command may fail with "Volume group not found"
error, or "Cannot change VG test while PVs are missing".

lvm fixed this issue in version 2.02.100-7.el6 by disabling udev cache,
setting obtain_device_list_from_udev to 0. Unfortunatlly, lvm fix is not
enough for vdsm, as the fix is applied only if no lvm.conf file exists.
When upgrading existing lvm installation, lvm creates a lvm.conf.rpmnew
file, and the system administrator is responsible for updating lvm
configuration.

This patch disable udev cache using the --config option, used to
override many other lvm options, ensuring proper configuration on both
new and upgraded systems.

Disabling udev cache may have minimal performance effect according to
lvm developers.

Change-Id: Ib55c8d444f3be9f63bfd23d8def60607b5b3dff0
Bug-Url: https://bugzilla.redhat.com/1014942
Signed-off-by: Nir Soffer <nsoffer@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/20890
Reviewed-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-by: Ayal Baron <abaron@redhat.com>
Reviewed-by: Allon Mureinik <amureini@redhat.com>