Jay Pipes c41db608fe Rework monitor plugin interface and API ...

In order to prepare for the stevedore-ization of the compute monitor
plugins, and to clean up the overly complex monitor API, this patch
breaks out the base monitor plugin into a much simpler class that has
the following methods:

- get_metric_names(), which remains unchanged in its
  purpose from the original ResourceMonitorBase class
- get_metric(name), which returns a (value, timestamp) tuple for
  a supplied metric name
- add_metrics_to_list() which is a non-overrideable method on the
  base plugin class that adds a set of metrics to a
  nova.objects.MonitorMetricList object supplied as the parameter

There is a base class called nova.compute.monitors.base.CPUMonitorBase
that simply returns the appropriate CPU monitor metric name constants
for the get_metric_names() method.

The directory structure of the monitor plugins and the module naming for
the lone in-tree is changed to better represent what the directories and
files contain. The lone in-tree plugin is a monitor that inherits from
nova.compute.monitors.base.CPUMonitorBase and uses the call to the
hypervisor's get_host_cpu_stats() to grab CPU-centric metrics on a
periodic basis.

Change-Id: I3f2e8eca6ce43b07b3c8b430b8576be4f0d3f909
Partial-bug: 1468012

2015-07-06 09:47:27 -04:00

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