Add the option of setting only Tor exit nodes (no VPNs)

[BBerastegui]

As proposed here: #6 (comment)

It'll be awesome to have the option of allowing doxycannon to pop only docker tor containers that will be used as round-robin outgoing proxies for Haproxy.

./doxycannon.py --only-tor --nodes 16

That will popup 16 tor docker containers that will be used as outgoing proxies for Haproxy.

[audibleblink]

@BBerastegui hey

i've submitted PR #25 if you wanted to review and test. I tried with 3 nodes and it worked. Let me know if you run into any issues.