LU-11128 ptlrpc: new request vs disconnect race

LU-11128 ptlrpc: new request vs disconnect race

new request can race with disconnect-by-idle process.
disconnect code detect this state and initiate a new connection.

Change-Id: I6acc913c371f2ae63f27151edce457c2a13118c5
Signed-off-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/32980
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mpershin@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>