.deployer-store-cache relies on ~/.juju

[Francis Ginther]

This was found while using the latest daily from ppa:ahasenack/juju-deployer-daily in a xenial environment using juju2. This environment has never been used with juju 1. The version is 0.7.0~bzr170~51~ubuntu16.04.1

Traceback (most recent call last):
  File "/usr/bin/juju-deployer", line 9, in <module>
    load_entry_point('juju-deployer==0.7.0', 'console_scripts', 'juju-deployer')()
  File "/usr/lib/python2.7/dist-packages/deployer/cli.py", line 138, in main
    run()
  File "/usr/lib/python2.7/dist-packages/deployer/cli.py", line 246, in run
    importer.Importer(env, deployment, options).run()
  File "/usr/lib/python2.7/dist-packages/deployer/action/importer.py", line 292, in run
    self.get_charms()
  File "/usr/lib/python2.7/dist-packages/deployer/action/importer.py", line 146, in get_charms
    no_local_mods=self.options.no_local_mods)
  File "/usr/lib/python2.7/dist-packages/deployer/deployment.py", line 188, in fetch_charms
    charm.fetch()
  File "/usr/lib/python2.7/dist-packages/deployer/charm.py", line 155, in fetch
    self._fetch_store_charm()
  File "/usr/lib/python2.7/dist-packages/deployer/charm.py", line 181, in _fetch_store_charm
    cache_dir = self._get_charm_store_cache()
  File "/usr/lib/python2.7/dist-packages/deployer/charm.py", line 208, in _get_charm_store_cache
    os.mkdir(cache_dir)
OSError: [Errno 2] No such file or directory: '/home/ubuntu/.juju/.deployer-store-cache'

juju 2 no longer creates ~/.juju, it uses .local/share/juju instead.

I missed this during the juju2 support work.

Manually creating ~/.juju works as a workaround.