Remove duplicate add_vrf and add echo

Echo function support sleeping for a specified amount of time so that it
becomes easier to test parallel requests.

Part of #273
Add basic parallel benchmark

This benchmark sends a bunch of requests in parallel to the nipap
XML-RPC API and measures the time taken to respond.

Part of #273
Switch to Tornado for running Flask

Tornado is essentially a small web server that can run Flask apps. This
switches to Tornado as Tornado can pre-fork a number of instances of our
app and serve them in parallel!

Part of #273
Install Flask-XML-RPC and Tornado

Hopefully fixes the Travis-CI build.

Part of #273