Introduce `tools/kolla` to interact with kolla

This is supposed to prevent proliferation of scripts in "tools"
directory and reduce code duplication.

This first patch replaces tools/{start,stop,pull,status} scripts and
more commands are to be added in the future.

Change-Id: I3d99cf5033be8631d8e6f32a4c34d3b5ffcae7e8