switch to T2_CH_CERN override catalog

Instead of using the T0_CH_CERN override catalog use the one for T2_CH_CERN
Merge pull request #4049 from hufnagel/t2-override

switch to T2_CH_CERN override catalog
support different scram archs for different Tier0 parts

Add a mandatory scram_arch parameter to the dataset configuration, this is passed to the PromptReco Spec and allows to use CMSSW releases that aren't available with the hardcoded default ScramArch.
Merge pull request #4050 from hufnagel/tier0-scram

support different scram archs for different Tier0 parts
fix problem with subscriptions of PromptReco data

Due to a typo, PromptReco data wasn't using the configured PhEDEx subscriptions. Fix this.
Merge pull request #4051 from hufnagel/promptreco-subscriptions

fix problem with subscriptions of PromptReco data