tarmac doesn't clean up /tmp usage correctly

[Andreas Hasenack]

We got into a situation where /tmp was using up 3.6Gb. It was full of temporary directories created by tarmac as bzr branches.

Looking at the code, it only tries to remove the temporary directory in __del__() method in the Branch class:

    def __del__(self):
        """Do some potenetially necessary cleanup during deletion."""
        if self.temp_tree_dir is not None:
            shutil.rmtree(self.temp_tree_dir)

Apparently that does not always run.

[dobey (dobey)]

For posterity, when running tarmac to land tarmac branches, the following occurs during tearDown of some of the tests:

Exception OSError: OSError(2, 'No such file or directory') in <bound method Branch.__del__ of <tarmac.branch.Branch object at 0x35b5690>> ignored

The tests pass and it appears __del__ is being called, albeit inconsistently. It's also still unclear why it wouldn't be called in normal usage, even in the worst case of when the python interpreter cleans up and exits.