Trick deployer into allowing abs path for charms

Deployer allows abs paths for branches but not for charms, but in order
to use a branch, the branch dir must be under vcs control. So we make
a bzr repo out of our local charm tempdir.
Improve bundletester output handling

In debug mode, allow bundletester stdout/stderr to write to stdout/stderr
on the parent process.

Also added special handling for bundletester exit code 3, which signifies
that no tests were found for the given target.