Fix initial DB schema migration

Currently, initial DB schema migration fails on MySQL and
PostgreSQL due to the following reasons:

  - resource_classes and flavors tables are created after ones
    referencing their columns with FKs are created

  - lenght of nova_flavor_uuid column (VARCHAR) is not specified

Also, a typo in the name of logger method exception() is fixed.

Change-Id: I4438a836a32860a5695bbf8eb60bd230034e1f98
Merge "Fix initial DB schema migration"