AutoCond magic to set global tag during PAT tuplization

cc @isobelojalvo

You can now automatically get a reasonable global tag (via [1]) when PAT-tuplizing.

Example:
```shell
"globalTag=autocond:startup_GRun"
```
 will use the startup_GRun key from from [1].

[1] https://github.com/cms-sw/cmssw/blob/CMSSW_5_3_X/Configuration/AlCa/python/autoCond.py