Add command line gcs tools

[delgadom]

would be great to do something along the lines of

rhg-compute-tools gcs rsync src dst

Which suggests we probably need a broader command line strategy for handling different submodules

[delgadom]

@brews if you want to throw in a click module for calling the function you just merged that would be killer!

[delgadom]

but only if you've got a bit of downtime

[brews]

@delgadom What tool would be most in demand? You got one good one in mind that I could start with?

What are we going for? Much of this looks like a gsutil clone, with a few exceptions like replicate_directory_structure_on_gcs().