Fix unschuduled mode when paths not to be run are created

[davidlange6]

Previous cmsDriver implementation assumed that all paths declared should be run in unscheduled. This is not the case, particular when AlCas are included (as there is one monolithic cff that makes many paths).

This commit fixes that problem by making an explicit schedule (which is later deleted but after the pruning is done)

[cmsbuild]

A new Pull Request was created by @davidlange6 (David Lange) for CMSSW_7_4_X.

Fix unschuduled mode when paths not to be run are created

It involves the following packages:

Configuration/Applications

@cmsbuild, @franzoni, @davidlange6 can you please review it and eventually sign? Thanks.
@ghellwig, @Martin-Grunewald 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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