XD-2426: Use new Travis CI build env, add caching

- test cache behavior
- Add debug
- use -PwikiBranch=origin/master
XD-2386 Acceptance tests for tcp-client source

connect to a nc (netcat) server that returns the following value UOHSO638abna9beqw12.
The netcat can be run using the following:
(Mac)
while true; do nc -l -c  8782 < index.html; done
(*nix)
while true; do nc -l -C  8782 < index.html; done

where index contains UOHSO638abna9beqw12

See spring-xd-integration-test/src/scripts for scripts that
launch the nc process as described above.
Comment out KafkaSourceSinkTests until XD-2502 is fixed