This inventory module is based on the shade library like the new os_
modules. It shares the ability to configure itself from os-client-config
configuration files or from the standard OS_ environment variables.
More importantly the guts of the code to get the server vars is now
shared with os_compute_facts. This means that playbooks that provision
compute hosts and then want to run plays on them can refer to server
variables in exactly the same way whether the provsioning play ran first
or whether the play ran in the context of a pre-existing inventory.
