FastTimerServiceClient: update plots after every lumisection

[fwyzard]

Adapt the DQM client to the updated DQMEDHarvesting interface, which is necessary to properly update histograms online, and in general when running the DQM harvesting with the "Online" convention.

If possible, this might be useful to have for MWGR#7.
It requires (and includes) #5303 .

[fwyzard]

+1

assuming it doesn't break anything

[cmsbuild]

A new Pull Request was created by @fwyzard (Andrea Bocci) for CMSSW_7_1_X.

FastTimerServiceClient: update plots after every lumisection

It involves the following packages:

DQMServices/Core
HLTrigger/Timer

@nclopezo, @danduggan, @rovere, @cmsbuild, @deguio, @ojeda can you please review it and eventually sign? Thanks.
@barvic this is something you requested to watch as well.
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@nclopezo, @ktf you are the release manager for this.
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[deguio]

+1
assuming the same

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_1_X IBs unless changes or unless it breaks tests. @Degano can you please take care of it?