vdsm: refactor buildConfDevices and getConfDevices into single function

Removes code duplication while flow should remain the same
- also removes getConfSmartcard call in buildConfDevices as this
call is obsolete (smartcard was introduced later and is therefore not
needed for backwards compatibility)

Change-Id: Ifd3a209967f97a55fe861c4446e8f93e1a1da08e
Signed-off-by: Martin Polednik <mpoledni@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/19348
Reviewed-by: Federico Simoncelli <fsimonce@redhat.com>