moved get_redis from db.py to routes/common.py

inventory_provider/db.py

inventory_provider/routes/classifier.py

inventory_provider/routes/common.py

inventory_provider/routes/data.py

inventory_provider/routes/opsdb.py

inventory_provider/routes/poller.py

test/per_router/test_data_routes.py

test/per_router/test_poller_routes.py

test/test_classifier_routes.py

test/test_external_inventory_routes.py