Replaces standard logging with common logging

Common modules can now safely import other common modules
since update.py will automatically install dependencies.

Change-Id: I0ad12d7e6e623657c40659aca4148439cd03d3fa
Removes created_at, updated_at from ModelBase

Created a 'TimestampMixin' class.
Next step is to update Nova which is the only project using oslo.db

Fixes bug #1119702

Change-Id: I1ffcc09a2971e6e6102da7ecb855a2837a159baf
Merge "Replaces standard logging with common logging"
Merge "Removes created_at, updated_at from ModelBase"