Merge lp://staging/~sinzui/juju-ci-tools/run-uitests into lp://staging/juju-ci-tools

Run Juju built from the release tar file in uitest.

This branch adds a script that runs uitest with the released GUI and juju built from the tar file.

Testing with the proper juju is hard because uitest ui test only supports testing git branches. this is bad because the tree contains undocumented deps and non-free content. The release tar file is purged of improper files. uitest might pass a Juju built from a branch if it requires a undocumented dep. uitest also taints the code to use a test charmstore.

The solution I took was to taint the unpacked file (so that we know exactly what is being tainted). We build the binaries outside of uitest. uitest will use found binaries when it can also confirm the source code is tainted.

I am unsatisfied with the setup of credentials in this script. We have never had need before now to re-use the deploy_stack.py env setup. Maybe this can be added in a future branch.

In a future branch, we will add support to test the charm plugin. The plugin has different dependencies than juju. Building from the release tar file conflicts with building juju from its deps. This underscores the problem that both juju and charm plugin have shared but divergent deps. We do want to test the charm plugin built for release with juju built for release and verify the plugin still works.