LU-793 ptlrpc: allow client to reconnect with RPC in progress

LU-793 ptlrpc: allow client to reconnect with RPC in progress

Since not letting clients with pending RPCs to reconnect caused a lot
of problems, this patch allows such a reconnection and would only
refuse to process requests with the same xids that are already being
processed.

Bulk requests are aborted upon reconnection by comparing connection
count of request and export.

Signed-off-by: Mikhail Pershin <mike.pershin@intel.com>
Change-Id: Ic4b23a71fd288df02d1040d98867373ae06b60f6
Reviewed-on: http://review.whamcloud.com/4960
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>
Reviewed-by: Alexander Boyko <alexander_boyko@xyratex.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>