dapltest: transaction test moves to cleanup stage before rdma_read processing is...

dapltest: transaction test moves to cleanup stage before rdma_read processing is complete

With multiple treads, the transaction server tread can move to cleanup
stage and unregister memory before the remote client process has
completed the rdma read. In lieu of a rewrite to add sync messages
at the end of transaction test phase, just add a delay before cleanup.

Signed-off-by: Arlin Davis <ardavis@ichips.intel.com>