LU-11131 target: keep reply data bit set on failover

LU-11131 target: keep reply data bit set on failover

The following scenario leads to failure of recent reint rpc:

1. mdt server has number of rpcs being handled, rpc 1 from client A
and rpc 2 from client B.

2. shutdown for the server starts

3. rpc 1 is processed, reply data is added, but client A gets ENODEV
in reply (ptlrpc_send_reply()) as shutdown is running

3. shutdown reaches class_disconnect_exports() and links an export A
to the list of zombie exports

4. obd_zombid thread wakes up and destroy the export A, which includes
freeing of reply data list with clearing bits in
lut->lut_reply_bitmap (tgt_free_reply_data())

5. export B is still processing the rpc 2 and looks for free bit in
the lut->lut_reply_bitmap to store reply data
(tgt_add_reply_data()). If it finds a bit which has been just freed by
obd_zombid thread, then reply data from export A will get overwritten
in reply_data file with reply data from export B

6. after failover, reply data gets restored with
tgt_reply_data_init(). The reply data of client A is missing

7. client A reconnects and resends its rpc 1. Server does not find
reply data and processes the rpc as if it has not been seen yet. In
case of unlink, the directory entry already does not exist so rpc 1
fails

The fix is to not free bits in lut->lut_reply_bitmap in case of
failover.

Test illustrating the issue is added.

Signed-off-by: Vladimir Saveliev <c17830@cray.com>
Cray-bug-id: LUS-6004
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-by: Andriy Skulysh <c17819@cray.com>
Tested-by: Elena Gryaznova <c17455@cray.com>
Change-Id: I6db3728f3271ce2751fbe08dadca365eb2ffe727
Reviewed-on: https://review.whamcloud.com/32798
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>