Force protocol when using get-deps. Usage: rebar get-deps protocol=http|...

Added this feature because from work I cannot access git URI:s outside of the intranet, and editing each deps configuration file by hand sort of sucks.

This forces rebar to use ssh, http or https by adding force_protocol=https when using get-deps.

It would'nt be hard to add support for the other CVS:s.

Let me know what you think!