LU-10286 mdt: deny 2.10 clients to open mirrored files

LU-10286 mdt: deny 2.10 clients to open mirrored files

2.10 clients would manipulate mirrored layout as PFL layout, which
would damage mirrored files.

This patch only allows mirrored files to be opened by clients who
understand mirror layout.

It also fixes the problem that it should check OBD_CONNECT_FLAGS2
first before checking OBD_CONNECT2_XXX flags.

Test-Parameters: envdefinitions=SLOW=yes clientjob=lustre-b2_10 clientbuildno=68 testlist=runtests,sanity
Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I3431211ad30a1edd07f0f583d573328d6308779d
Reviewed-on: https://review.whamcloud.com/30957
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Tested-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>