run: params are not checked before running the command

[skshetry]

$ dvc run -n train1 -d users.csv -p tr_conf.yaml:epochs1,log_file,dropout -M e1/summary.json -m e1/logs.csv -o e1/logs python train.py
.... training is happening
.... 27 hours latter:
60000/60000 [==============================] - 6s 94us/sample - loss: 0.0588 - accuracy: 0.9806 - val_loss: 0.0707 - val_accuracy: 0.9821
ERROR: failed to run command - Parameters 'epochs1' are missing from 'tr_conf.yaml'.