reuse cluster for TFsShellTest and made each test isolated
TachyonFSTest now uses a shared cluster to speed up test run times
Cut FileInStreamTest time in 1/3 by making cluster shared between tests
Cut RemoteBlockInStreamTest run time by 1/4th by reusing the cluster between runs
Changed LocalBlockInStreamTest to use local cluster, cutting the time to run in thirds
Merge pull request #570 from dcapwell/testSpeedupImprovments

reuse cluster for TFsShellTest and made each test isolated