Install PycURL, required by apt_repository

Install the `python-pycurl` APT package, which is required by
apt_repository.

Without this, adding the Docker repository currently fails with:

```
msg: Could not import python modules: pycurl. Please install
python-pycurl package.
```
Install docker-py as required by docker module

Install `docker-py` using `pip` as required by Ansible's docker
module[1].

[1]: http://docs.ansible.com/docker_module.html
Merge branch 'install-dockerpy'