Parallels provider support

I've updated all the templates, vagrantfiles, and the makefile to add support for parallels.  I have one known issue with it, the parallels tools don't always install correctly.  Granted since parallels can't run headless, it's a pretty simple work around to install them manually.  

To be consistent, this should read:
````
-test -f .keep_known_hosts || rm -f ~/.ssh/known_hosts
````