make_client is a great, simple yet flexible way to get a fully featured
Client object. simple_client is similar for Session objects, but lacks
the argparse and arbitrary kwargs that make_client - plus it has a weird
name. Since adding those two features to make_client did not make it too
confusing - do the same for simple_client. Also, rename it to
session_client (with a backwards-compat alias) and add it to the README
docs.
In the process of doing this, extract the "get me a cloud config"
functinality into an additional helper function - get_config.
Change-Id: Iadd24dfa021f870b3e5858bab8cd91fc96a373c2
7a4993da41