Add support for VM monitoring

This patch gives the Monasca Agent the ability to monitor virtual
machines (VMs) provisioned under Nova.  It bundles Ceilometer's
virtualization inspector to gather the actual metrics, includes a
monasca-setup plugin, and adds cross-tenant support.  The latter
enables the Agent to submit metrics on behalf of a different
tenant/project, giving the VM's owner a set of metrics without each
VM having to run its own Agent.  This plugin collects two sets of
measurements per metric: one for the VM's owner (in-cloud) and for
the Operations team (infrastructure).  They differ in the following
ways:
- Operations metric names are prefixed with "vm." in order to group VM
  and overcloud metrics separately
- Operations metrics include "tenant_id" as a dimension
- Operations metrics include "cloud_tier" dimension with the value
  "overcloud"
- The "hostname" dimension for Operations contains the name of the
  compute server; for the tenant, "hostname" is the name of the VM

The metrics gathered by this plugin include:
- Disk I/O: read/write operations/bytes per second
- Disk I/O: errors per second
- Network I/O: in/out packets/bytes per second
- CPU utilization as a percentage of CPU time over polling time

Change-Id: I23781a1ba552ef2551e6ff1caea21dd8f515d73d