Tests: Add alembic to pylint ignores
Tests: Add alembic to pylint ignores

Add alembic.context and alembic.op to pylint ignore
list.  These are dynamic modules that pylint can't
process, generating many false positive pylint errors.

Change-Id: Icb4c0b5cbba02c42e9e2ee381dc9152f1c1de22c

openstack/cinder,mahak/cinder,mahak/cinder,openstack/cinder