Update swift pollster to use cache

Use the pollster cache to store the list of tenants
and the information swift has about them.

blueprint one-meter-per-plugin

Change-Id: I2c1fbbb99b2ae4796720ec6b7ac94ac27ab9ba5c
Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>
Merge "Update swift pollster to use cache"