Bug fix for getting Sequence labels

[SusieMurphy]

Bug fix for how labels are obtained and error handling added for cases of unexpected failure, so that other files are still calculated.

[cmsbuild]

A new Pull Request was created by @SusieMurphy for CMSSW_7_0_X.

Bug fix for getting Sequence labels

It involves the following packages:

FWCore/Utilities

@cmsbuild, @Dr15Jones, @ktf, @nclopezo can you please review it and eventually sign? Thanks.
@wmtan this is something you requested to watch as well.
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@ktf you are the release manager for this.

[cmsbuild]

-1
I ran the usual tests and I found errors in the following unit tests:

---> test testFWCoreUtilities had ERRORS

you can see the results of the tests here:
https://cmssdt.cern.ch/SDT/jenkins-artifacts/pull-request-integration/PR-1607/1510/summary.html

[Dr15Jones]

That error is not related to the code change. It is a spurious bug in the actual test.