Make nova-api logs more useful

The current logs make it hard to identify what API command is actually
being called, especially for POST, where the action is in the body.

* Whenever there is body, log it (info level)
* Log what function the API command maps to (debug level)

Change-Id: Ief14186b94e321d97575ee25e3507d3fc0178de6
Merge "Make nova-api logs more useful"