Ability to run tests in parallel

[marceloleitner]

Currently the suite runs test by test till the end, but we can save time by running some tests in parallel.
Pretty much what make -j would do. If doing some quick sanity checks, it would be fine even to overload the host with the tests. Seems only the repeatability ones would get affected.
This should be feasible by adding a prefix to the netns names and buffering the logs for each job, and then generating a final one. (or something like that)

[marceloleitner]

Cc @lxin

[lxin]

My understanding for running tests in parallel is that we schedule the different cases into the different threads, but one case can be only running in one thread at the same time. If so, now all users have to do is to pass $TestCase and $O to ./sctp-tests, no need to add anything more. But yes, if you wish that users can pass '-j n', then ./sctp-tests dispatches by its own, we need to do something for it.