feature: support processing raw measures on GET

[gordon chung]

a large number of metricd workers is required to keep processing all metrics at a timely rate. i think it'd be cool if we could allow users to deploy less metricd workers and on GET, check to see if there are unprocessed measures and process on GET. this would sacrifice response time but would allow for smaller deployment requirements

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/351758

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/351758
Committed: https://git.openstack.org/cgit/openstack/gnocchi/commit/?id=72a2091727431555eba65c6ef8ff89448f3432f0
Submitter: Jenkins
Branch: master

commit 72a2091727431555eba65c6ef8ff89448f3432f0
Author: gord chung <email address hidden>
Date: Fri Aug 5 09:47:09 2016 -0400

    add support to process measures on GET

    depending on the backlog, the returned measures from get-measures
    may not include what sits in carbonara backlog. to allow for more
    flexibility on metricd deployments, this patch offers the ability
    to allow users to get all measures even if they don't have enough
    metricd workers, at the expense of responsiveness.

    refresh blocks until it can process measures

    Change-Id: I588ae6879474d780e8ec9e893d4ecc2b367b832e
    Closes-Bug: #1603495