SQL client E2E test is missing dependencies

https://travis-ci.org/zentol/flink-ci/builds/411668376

The sql-client end-to-end test uses the dependency-plugin to copy a few jars into the /target directory. However since the module doesn't define dependencies on these jars there's no guarantee that these jars are built before the test, or even at all. This caused the tests to fail, since the kafka 0.11 connector wasn't at all and also wasn't available in the SNAPSHOT repository.