Rename references to compute networks client

The single network client is going to be split out into multiple
clients, one of which will be called NetworksClient. This patch
renames references to the compute networks client (networks_client)
to avoid confusion or conflicts with the new networks client.

Partially implements blueprint consistent-service-method-names

Change-Id: I1730adb3258557698dbe15658bb1c12f2292c2fd
7 files changed