vm: rename _updateDrive to updateDriveParameters

As preparation for change I472c2931 the method _updateDrive is renamed
to updateDriveParameters to avoid confusion with updateDriveVolume.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=923964
Change-Id: Ic60f1e0bcd889dffba9003d413fa305f6102eccf
Signed-off-by: Federico Simoncelli <fsimonce@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/13631
Reviewed-by: Ayal Baron <abaron@redhat.com>
Reviewed-by: Yeela Kaplan <ykaplan@redhat.com>
Tested-by: Dafna Ron <dron@redhat.com>