Break up compute pollsters

Break the compute pollsters up into separate plugins.  This is
submitted as one patch for all of the compute pollsters because
they are moved into a new package to make the files a little easier
to manage.

blueprint one-meter-per-plugin

Change-Id: Ibc6a9c3f73594c94b578f4229e1f9e9c941c7f4f
Signed-off-by: Doug Hellmann <doug.hellmann@dreamhost.com>
Merge "Break up compute pollsters"