Update compute CPU pollster to use cache

Use the pollster cache to store the CPU statistics
for an instance. Eventually the single pollster will
be broken up into separate pollsters that all use
the cache.

blueprint one-meter-per-plugin

Change-Id: Iada02930867c09d05684ba0acea728d0d1cf06ae
Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>
Merge "Update compute CPU pollster to use cache"