Adds cluster support, allows tsuru-now installed under Debian wheezy

Added cluster support to tsuru-now. We can now use `--template` to specify the roles of server to be installed.

Other features like `--ext-repository`, to use an external repository (like `http://philiptzou.github.io/tsuru-deb/`) instead of tsuru/ppa.

`--verbose`, to print detailed information for debugging.
Nevermind, Go will create it.