Update Salt's virtualenv settings

1) no_site_packages option has been deprecated for system_site_packages
2) if the requirements file has references to other requirement files on the file system, Salt will break unless no_chown option is given which prevents Salt from copying the requirements file to /tmp/ before running.
Make uWSGI directory apps-available.

Not sure if something changed in PyPI or Ubuntu packages, but the
/etc/uwsgi/apps-available directory stopped being auto-created
which causes other uWSGI salt tasks to fail.
Merge pull request #15 from sauerc/fixup-venv-settings

Update Salt's virtualenv settings
Merge pull request #16 from sauerc/fixup-uwsgi-dir

Make uWSGI directory apps-available.