LU-9899 tests: mount client on MGS for tests with pools

LU-9899 tests: mount client on MGS for tests with pools

When a Lustre file system has the MGS and MDS on separate
nodes, the file system must be mounted on the MGS to allow
OST pools to work properly.

There are several tests that deal with creating, adding
to and deleting OST pools. Create functions to mount and
unmount the file system on the MGS in test-framework and call
these functions when necessary for the Lustre test suites
conf-sanity test 82b, 103
sanity tests 27D, 200, 220, 406 and
replay-single test 85b.

Test-Parameters: combinedmdsmgs=false testlist=sanity,replay-single,conf-sanity

Signed-off-by: James Nunez <james.a.nunez@intel.com>
Change-Id: I4b3e331b8d1ea6c3f8c9ea8a571e26f66f4535f8
Reviewed-on: https://review.whamcloud.com/28806
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>