Remove leftover logback-test.xml in flink-java8.tests
Point quickstart scripts to 0.6.1-incubating
Change logging backend of SLF4j from Logback to Log4j for better compatibiltiy with YARN.
We'll still ship the Logback configuration file and pass them their path to the JVM so that
users can use Flink with Logback as well.

This closes #125