Add a config.sh for shared variables between provisioner scripts

[lo5an]

What about adding a config.sh to make it easier to use variables across the scripts? In particular, it'd be nice to be able to set the various installation paths in one place and refer to them from the various scripts.

[whikloj]

I am working on this, still need to test but I couldn't assign this to myself.
https://github.com/whikloj/islandora_vagrant/tree/issue-20

[ruebot]

Now you can!

(I forgot to add this repo to the team.)

[lo5an]

Great!