Remove sql.Base.get_session

With the change to use oslo's db.sqlalchemy.sessions, the
sql.Base class isn't doing enough to justify its continued
existence.

This change is removing the get_session member, which was just
a new name for openstack.common.db.sqlalchemy.session.get_session() .

Part of bp use-common-oslo-db-code

Change-Id: I083ecd54200dcd6cae7248d1a6ef4fcec64e6589
Move sql.Base.transaction

With the change to use oslo's db.sqlalchemy.sessions, the
sql.Base class isn't doing enough to justify its continued
existence.

This change is moving the transaction member out of Base.

Part of bp use-common-oslo-db-code

Change-Id: Ie0df7b397f8508e1c9be70ce9bbb2d733bde03ea
Don't mask the filter built-in

There was an argument to a function called 'filter'. 'filter' is a
python built-in, so that name shouldn't be reassigned
to something else since that will mask the built-in which can be
confusing and problematic when someone wants to use the built-in.

Also, changed the name of the sql.Base member to filter_query for
the same reason.

Change-Id: I8eb13c73bd8cf0f31e08951bc0fcaf49abd49ef1
Merge "Remove sql.Base.get_session"
Merge "Move sql.Base.transaction"
Merge "Don't mask the filter built-in"