Instead of flushall, do selective db flush, as we are now sharing the same redis instance as analytics

Problem:
On restart of contrail-webui-middleware service, all the redis dbs are flushed.
If the webui runs on the same node as analytics, then the restart of contrail-webui-middleware
service would flush the db created by analytics node, where the UVEs are cached.

Fix:
contrail-webui-middleware service should flush only the dbs created/owned by webui and not all the dbs.

Change-Id: I907045f70b63af106ee553eb055ebd863894b52e
(cherry picked from commit a8351cb6734ca1062dde9bc284432efd98eb44be)