Python 3, PEP-8, docs, and more

[codekoala]

I've done a fair mount of refactoring to the script here. Some of the highlights:

• less dependent upon a specific filesystem layout
• should work with both Python 2 and 3 now
• reduced redundancy in a few places
• added a check to see if haproxy is installed before running
• restarting haproxy directly with the subprocess.call function, rather than using it to call a shell script
• some PEP-8 items
• lots of docstrings... I hope they're accurate enough for you