Vague error when no metrics in Usage panel

[Rob Raymond]

When you have ceilometer configured but there are no metrics, you get the error message:
Error: An error occurred. Please try again later.

It would be better to give the user a warning that there are no metrics.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/70391

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/70391
Committed: https://git.openstack.org/cgit/openstack/horizon/commit/?id=cb425647838048c1401ad6371ad9529ccb37687e
Submitter: Jenkins
Branch: master

commit cb425647838048c1401ad6371ad9529ccb37687e
Author: Rob Raymond <email address hidden>
Date: Thu Jan 30 23:41:31 2014 -0700

    Warn user when no meters in metrics panel

    Avoid generating an exception by first checking if there is a
    meter before calling replace method on it.
    Give the user a nice warning if there are no meters available. This cannot be
    done in the get method because this is an AJAX call to fetch JSON data.

    Change-Id: I1536474c85083fb0bb3876e6650a3c928625a5c5
    Closes-bug: #1274823