run: ui issue for run

[skshetry]

1. Eg:

$ dvc run -n train ...
ERROR: failed to run command - Stage with name 'train' already exists in 'pipelines.yaml'.

There's no need for failed to run command because the commands were never run and is a bit unnecessary.

$ dvc run -n train1 -d users.csv -p tr_conf.yaml:epochs,log_file,dropout -M summary.json -m logs.csv -o logs python train.py
ERROR: failed to run command - file/directory 'summary.json' is specified as an output in more than one stage:
	pipelines.yaml:train
This is not allowed. Consider using a different output name.

Suggestion:

ERROR: output 'summary.json' already exist on stage 'pipelines.yaml:train'.

$ dvc repro pipelines.yaml
ERROR: you've introduced a cycle in your pipeline that involves the following stages:
	- pipelines.yaml:train
	- pipelines.yaml:process

Suggestion:

ERROR: output 'IN.TSV' introduces a cycle that involves stages: train, process