Add pipeline support to s_server and s_client

Add pipeline support to s_server and s_client

Add the options min_send_frag and max_pipelines to s_server and s_client
in order to control pipelining capabilities. This will only have an effect
if a pipeline capable cipher is used (such as the one provided by the
dasync engine).

Reviewed-by: Tim Hudson <tjh@openssl.org>