LU-9795 gss: properly handle mgssec

Secured connection to MGS must have all 3 root, mds and oss flags set
by convention.

Also add regression tests for mgssec in sanity-sec.

Test-Parameters: testlist=sanity-sec envdefinitions=ONLY="32 33",SHARED_KEY=true
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: I655913b15a551c205cdc3e16fffd48193c8da1fe
Reviewed-on: https://review.whamcloud.com/33357
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Jeremy Filizetti <jeremy.filizetti@gmail.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>