better propolis server management.

[rcgoodfellow]

As noted here our management of the propolis binary is pretty fragile.

There is a fragile bash script to download propolis. It also installs propolis-server to a global location which is not good for multi-user environments. Falcon should store propolis-server in a user-local location, or even a topology local location like .bin/proplis-server and automatically download the correct version if it's not there.