minimise hmac calls to avoid performance degradation

[gordon chung]

when publishing data to the queue, datapoints are run through hmac to generate a secure signature. this process is expensive

for example, in event endpoint:
event_converter ~= 1ms/event
broadcast w/out hmac ~= 60ms/event
broadcast w/ hmac ~= 12ms/event

we should minimise the use of signature

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/167690

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/167853

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/167690
Committed: https://git.openstack.org/cgit/openstack/ceilometer/commit/?id=f75a05091082abeeb8f0cc6d0c4d66b0e320f6d7
Submitter: Jenkins
Branch: master

commit f75a05091082abeeb8f0cc6d0c4d66b0e320f6d7
Author: gordon chung <email address hidden>
Date: Tue Mar 24 18:02:34 2015 -0400

    minimise the use of hmac

    - computing a signature from hmac requires significant overhead.
    don't compute it for each pipeline.
    - also adds in missing support to verify signature at pipeline.

    Change-Id: Idfec6dfb645d581f6bc55264a042f6792c26df75
    Partial-Bug: #1436077

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/167853
Committed: https://git.openstack.org/cgit/openstack/ceilometer/commit/?id=761360e570393bde51c88a4ac0a633d43a65308f
Submitter: Jenkins
Branch: master

commit 761360e570393bde51c88a4ac0a633d43a65308f
Author: gordon chung <email address hidden>
Date: Wed Mar 25 21:17:38 2015 -0400

    support ability to skip message signing

    there is significant overhead in signing each datapoint. this patch
    adds support to skip signing messages by setting the telemetry_secret
    empty for users who do not need signing or where MQ security is enough.

    DocImpact
    Closes-Bug: #1436077

    Change-Id: Iec0b995e511085fdce1fc5f9286fddd25ab701f0