reuse cluster for TFsShellTest and made each test isolated

Cut TFsShellTest from 6 minutes to 30 seconds.  Same trick can be used for all long running tests.
Where is this documented and why? It's more logical to have before...
Before after.
On Dec 21, 2014 11:12 AM, "Haoyuan Li" <notifications@github.com> wrote:

> In core/src/test/java/tachyon/client/FileInStreamTest.java
> <https://github.com/amplab/tachyon/pull/570#discussion-diff-22149516>:
>
> >      System.setProperty("tachyon.user.quota.unit.bytes", "1000");
> >      System.setProperty("tachyon.user.default.block.size.byte", String.valueOf(BLOCK_SIZE));
> > -    mLocalTachyonCluster = new LocalTachyonCluster(10000);
> > -    mLocalTachyonCluster.start();
> > -    mTfs = mLocalTachyonCluster.getClient();
> > +    CLUSTER = new LocalTachyonCluster(10000);
> > +    CLUSTER.start();
> > +    TFS = CLUSTER.getClient();
> > +  }
> > +
>
> minor style issue. after() should be ahead of before()
>
> —
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> <https://github.com/amplab/tachyon/pull/570/files#r22149516>.
>