jvpp: test measuring number of invocations per time (VPP-619)

jvpp: test measuring number of invocations per time (VPP-619)

test provide two ways to count invocations:
1) maximum number of invocations and received replyies within 1 sec
2) measure time in ns from first request to receiving last reply
over set amount of requests
specific command is included in Readme
results from testing on my local machine were:
350K/sec Callback Api Read - show version
250K/Sec Future Api Read - show version
120K/sec allback Api Write - add table

Change-Id: Ie0383d848b98ee2b4b90c38a827a24acd28cac72
Signed-off-by: Matej <matej.perina@pantheon.tech>