LU-1943 tests: Allocate sequences on MOUNT2 in replay_barrier()

LU-1943 tests: Allocate sequences on MOUNT2 in replay_barrier()

Port of ORI-448 to the master

In order to avoid sequence file updates after a target is made
read-only, replay_barrier() creates a file in "MOUNT" on every
client node. This is not enough because the "MOUNT2" clients may
also trigger sequence file updates. This patch makes sure the trick
is applied to "MOUNT2" clients as well.

Change-Id: I832689a2d2ca205d927bc5d0a15ab14fceb3bf80
Signed-off-by: Li Wei <liwei@whamcloud.com>
Reviewed-by: Mikhail Pershin <tappro@whamcloud.com>
Signed-off-by: Mikhail Pershin <tappro@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/4196
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>