Add spec about central and compute agents merge

As currently we are having unified discovery and polling process,
we may merge compute and central agent to one configurable piece of
code, that will depend actually only on the meters to collect,
no matter if it will be running on the compute node or cloud
controller.

Change-Id: I2fa29cf51b426c27c951bf6275bcc6d5565bcf5a
Merge "Add spec about central and compute agents merge"