Update git submodules

* Update nova from branch 'master'
  to 9c2d9fd1eb5bbfd32fb99f367d0da1d1de51c330
  - Merge "db: De-duplicate list of removed table columns"
  - db: De-duplicate list of removed table columns
    
    We have a policy of removing fields from SQLAlchemy models at least one
    cycle before we remove the underlying database columns. This can result
    in a discrepancy between the state that our newfangled database
    migration tool, alembic, sees and what's actually in the database. We
    were ignoring these removed fields (and one foreign key constraint) in
    two different locations for both databases: as part of the alembic
    configuration and as part of the tests we have to ensure our migrations
    are in sync with our models (note: the tests actually use the alembic
    mechanism to detect the changes [1]). De-duplicate these.
    
    [1] sqlalchemy/alembic#724 (comment)
    
    Change-Id: I978b4e44cf7f522a70cc5ca76e6d6f1a985d5469
    Signed-off-by: Stephen Finucane <stephenfin@redhat.com>