Add a tool to run tests automatically on change

Add a tool to run tests automatically on change

While developing, its quite helpful to have relevant run automatically on
any changes. The script proposed here will do exactly that, using iwatch
(so it will only work on Linux systems).

https://code.launchpad.net/~clint-fewbar/juju/add-testrunner/+merge/128356

(do not edit description out of merge proposal)

[clint.byrum, 2012-10-06 15:49:49]

Please take a look.

[jimbaker, 2012-10-25 16:26:46]

Some minor issues I observed in trying this useful utility out:

1) eatmydata and iwatch need to be installed in advance; this issue is more
pronounced for eatmydata since it will fail in the test phase. I'm not certain
what the best approach is for this juju package. Perhaps just test installation
of both tools before running, as opposed to making this a requirement of juju
itself.

2) At least on my desktop, the test is always run twice, because iwatch seems to
pick up the file change twice.

3) Users need to remember they have this utility running and not attempt to run
more tests simultaneously, otherwise both  test runs will now fail.