Change oslo log imports to be consistent

In solum/api/auth.py, oslo log was imported as "log" and in other files
oslo log is imported "as logging". Change it to be consistent with the
rest of the code for easier searching and code consistency.

Change-Id: I9091f6f51c447d8646cb8a3aa8fae4fed5aea56b
Merge "Change oslo log imports to be consistent"