[FLINK-1054] Fix job history view in web frontend
Run tests in parallel

This uses the forkCount parameter of surefire/failsafe. This also
changes the JVM memory size for the testing VMs so that more can fit
into memory.

For this to work, NepheleMiniCluster must recognize when it is run in
a parallel testing environment and change ports accordingly. Also
AbstractTestBase and TaskTestBase must prefix temp files with the class
name to prevent name clashes.

This closes #96