Made file access in SimHitPrinter thread safe

[cmsbuild]

Since multiple instances of SimHitPrinter all share the same output
file via a static and those instances can be running on different
threads the file has to be protected by a mutex. In addition,
the creation of the file itself is done in a thread safe way.
Automatically ported from CMSSW_7_5_X #9723 (original by @Dr15Jones).

[cmsbuild]

A new Pull Request was created by @cmsbuild for CMSSW_7_6_X.

Made file access in SimHitPrinter thread safe

It involves the following packages:

SimG4CMS/Muon

@cmsbuild, @civanch, @mdhildreth can you please review it and eventually sign? Thanks.
@makortel this is something you requested to watch as well.
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@Degano you are the release manager for this.
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[civanch]

please test

[civanch]

+1

[cmsbuild]

The tests are being triggered in jenkins.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_6_X IBs or unless it breaks tests.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_6_X IBs or unless it breaks tests.

[cmsbuild]

This pull request is fully signed and it will be integrated in one of the next CMSSW_7_6_X IBs or unless it breaks tests. This pull request requires discussion in the ORP meeting before it's merged. @davidlange6, @Degano, @smuzaffar

[davidlange6]

+1