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.
Ah, that makes sense. I don't know of any better tool for the job then, offhand. Maybe this code is more clear? I definitely understand why ping is being used now.

```python
>>> ping_result = '64 bytes from 74.125.228.65: icmp_seq=1 ttl=54 time=44.8 ms'
>>> re.search('\d+ bytes from (.*):', ping_result).group(1)
'74.125.228.65'
```

That `ping_result` can be gained by issuing `ping -n -c 1`. The `-n` option puts ping in numeric mode, which prevents ping from resolving names.