rdma ioengine improvement

rdma ioengine improvement

1) Use fio shipped reentrant and thread-safe rand to replace buggy rand().
2) Add a pause time period before client start committing IOs.
	In SEND/RECV test, it's a good practice to setup the iodepth of
	of the RECV side deeper than that of the SEND side to
	avoid RNR (receiver not ready) error. The
	SEND side may send so many unsolicited message before
	RECV side commits sufficient recv buffers into recv queue.
	This may lead to RNR error. Here, SEND side pauses for a while
	during which RECV side commits sufficient recv buffers.
3) Fix server thread hanging bug.
	For RDMA WRITE/READ test, No IO bytes are accumulated in server side
	during test. Server thread indicates its task completion by changing
	its state into `done' as an alternitive. Add `td->done' checking in
	do_io().
4) Some comments revision.
	export EXTFLAGS and EXTLIBS with '+=".
	explanation on exchanging steps of RDMA ioengine control messages.

All these changes are tested in 40Gbps RoCE and 56Gbps InfiniBand testbeds.

Signed-off-by: Jens Axboe <axboe@kernel.dk>