LU-7543 obd: reserve connection flag OBD_CONNECT_SUBTREE

LU-7543 obd: reserve connection flag OBD_CONNECT_SUBTREE

The connection flag OBD_CONNECT_SUBTREE will be used for the
following the patch: LU-28 mounting of filesystem from MDS
http://review.whamcloud.com/5007

Land the connection flags to master earlier for reserving the
slot to avoid potential conflict with others.

Signed-off-by: Fan Yong <fan.yong@intel.com>
Change-Id: I61dad4ff22caf6ab933f38112f2f6e30fc5b9f3e
Reviewed-on: http://review.whamcloud.com/17644
Tested-by: Jenkins
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Patrick Farrell <paf@cray.com>
Tested-by: Maloo <hpdd-maloo@intel.com>