Add option parsing for Ansible's "run as" options

To allow specifying the remote user.

Also change shebang to use env, as Ansible's binaries used on the master
do (`ansible` and `ansible-playbook` -- modules use /usr/bin/python for
remote execution, override-able with `ansible_python_interpreter`).
Add `do` commands for the run-as options
Merge pull request #11 from ches/run-as-options

Add option parsing for Ansible's "run as" options