Clear hash ring cache in get_topic_for*

This causes the hash ring to be reset on each API request, avoiding
an issue where a new conductor never joins the ring until the API
service is restarted.

Closes-Bug: 1378570

Change-Id: Ic57370163f2f833efab662837036298f29f4ca90
Add SNMP driver for Aten PDU's

Closes-Bug: #1383162

Change-Id: I5b7c61c608fb32d7e35acfcd3f4bf5fec7c05b62
Merge "Add SNMP driver for Aten PDU's"