When the collector service is restarted, contrail-analytics.rules takes care of flushing the UVE db in redis.
However, when supervisor-analytics service is restarted, then old UVEs remain in the redis.
This is because redis is no longer part of the supervisor-analytics.
Therefore, flush the UVE db from redis when collector connects to redis for the first time.
Closes-Bug: #1347133

Change-Id: If6a455f074b34499827201793fa20d7c7f3c91ea
Merge "When the collector service is restarted, contrail-analytics.rules takes care of flushing the UVE db in redis. However, when supervisor-analytics service is restarted, then old UVEs remain in the redis. This is because redis is no longer part of the supervisor-analytics. Therefore, flush the UVE db from redis when collector connects to redis for the first time. Closes-Bug: #1347133"