HI relvals broken by TP.

[ktf]

Looks like #1200 broke HI workflows. See for example here.

I.e.:

----- Begin Fatal Exception 01-Nov-2013 08:12:42 CET-----------------------
An exception of category 'ProductNotFound' occurred while
   [0] Processing run: 1 lumi: 5 event: 5
   [1] Running path 'prevalidation_step'
   [2] Calling event method for module HitPixelLayersTPSelection/'primaryChgSimTracks'
Exception Message:
Principal::getByLabel: Found zero products matching all criteria
Looking for type: std::vector
Looking for module label: mix
Looking for productInstanceName: MergedTrackTruth

   Additional Info:
      [a] If you wish to continue processing events after a ProductNotFound exception,
add "SkipEvent = cms.untracked.vstring('ProductNotFound')" to the "options" PSet in the configuration.

----- End Fatal Exception -------------------------------------------------

@fabiocos @civanch @mdhildreth can you please look into it? Thanks.

[fabiocos]

Please pick #1288 tested to fix workflow 140