run simple_test twice.

Allows us to check if opening multiple connections works.
Forgot netconn_close at the end of simple test.
Added a count of run tests.
do not run fragmented packet test yet.
Fix race condition with echo server.

When we init the client IP stack, the server can finish its own init,
due to the way FIFOs are handled. This could lead to some race
conditions if the client started sending packets before the server was
ready to accept them.
typo fix.
added automated unit testing to travis ci.