Clean up the junk spewed by the flocker.volume.functional.test_script suite

[exarkun]

Replaced by https://clusterhq.atlassian.net/browse/FLOC-171

Many of these dump stuff onto stderr. For example:

  ReceiveTests
    test_creates_files ... cannot open 'testpool_c7fb14d9-49d5-4a3e-ad35-4043e6f281a9/e68b4669-9884-476f-a4ec-c551c0788c94.thevolume': dataset does not exist
[OK]

[wallrj]

See #183 (comment) for another example of this.

[exarkun]

Capturing stdout and stderr from child processes is mostly just a matter of passing the right arguments to Popen (or check_output or spawnProcess). We should do this so we capture this output in memory (probably by way of some kind of file object, since that's how all these APIs work). Then we can dump the information from memory into an appropriate log.

[adamtheturtle]

We are moving our development planning to JIRA. This issue is now being tracked at https://clusterhq.atlassian.net/browse/FLOC-171. You are welcome to file additional issues in GitHub if that's easier for you.