Allow users to configure the CM pipeline interval

The patch allows users to configure the ceilometer pipeline interval.
In localrc, we can add CEILOMETER_PIPELINE_INTERVAL=10 to handle the
pipeline each 10 seconds instead of the default 10 minutes.

Change-Id: Ic5216adbdfd70ade38912871ac6df3be732bf780
Merge "Allow users to configure the CM pipeline interval"