Changed implementation of proxy setup

Changed the setup_http_proxy method to setup_proxy.
The same arguments are used as before. This change includes
workarounds for pulp proxy configuration. However, until BZ1114083
is fixed, easier proxy support will not be possible.
Assigning logically distinct values to the same variable is totally legal bit a bit awkward. What do you think about something like this? Note that I'm calling the result `sat_ip` instead of `eth`, but that's just my best guess. I'm not 100% certain of the intent of this code.

```python
sat_ip = search(
    r'\d+ bytes from (.*):',
    run('ping -c 1 -n $(hostname) | grep "icmp_seq"')
).group(1)
```