MRP-1102 NULL pointer dereference in server_start_mgs

use error code from server_register_mount() to
print LCONSOLE_ERROR_MSG

Change-Id: I6da1786754a3a3f9c9a183fd8b1b3581eef23f29
Signed-off-by: Andriy Skulysh <Andriy_Skulysh@xyratex.com>
Reviewed-on: http://es-gerrit.xyus.xyratex.com:8080/539
Reviewed-by: Alexey Lyashkov <alexey_lyashkov@xyratex.com>
Reviewed-by: Alexander Boyko <alexander_boyko@xyratex.com>
Tested-by: Jenkins
Tested-by: Elena Gryaznova <elena_gryaznova@xyratex.com>
Reviewed-by: Vitaly Fertman <vitaly_fertman@xyratex.com>