LU-424 tests: conf-sanity test 55, 56, 58 failure fixes

LU-424 tests: conf-sanity test 55, 56, 58 failure fixes

The MGS service was not started in conf-sanity test 55, 56 and 58
with separate MGS and MDT configuration. This patch fix the issue.

Signed-off-by: Yu Jian <yujian@whamcloud.com>
Change-Id: Id82121f645d1903934bcf00328627947e943c45c
Reviewed-on: http://review.whamcloud.com/955
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Bobi Jam <bobijam@whamcloud.com>
Reviewed-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>