Fix when unschedule mode and customise_command are used together

customise_commands will fail in unschedule mode because it's called before the module is load.

https://github.com/cms-sw/cmssw/blob/CMSSW_7_2_X/Configuration/Applications/python/ConfigBuilder.py#L2211-L2226

For example,
cmsDriver.py step3 --filein file:MUO-Phys14DR-00003_step2.root --fileout file:MUO-Phys14DR-00003.root --mc --eventcontent MINIAODSIM --runUnscheduled --datatier MINIAODSIM --conditions PHYS14_25_V1 --customise_commands 'process.patJetPartons.partonMode = cms.string("Pythia6")' --step PAT --python_filename MUO-Phys14DR-00003_3_cfg.py --no_exec --customise Configuration/DataProcessing/Utils.addMonitoring -n 20