Graceful failure when --hosts=(nothing) is provided

[emayssat-ms]

AWS_PROFILE=7009 REGION=us-west-2 testinfra --capture=fd --connection=paramiko --sudo --hosts= -m "common or safeview or master" --maxfail 999 --tb=long --configuration-file configs/700995487849/Release/001e/config.yml --deployment-id default test_suite/

A command like the one above generates a lot of output when the problem is only due to the --host parameter is not set correctly. A simple validation check on the input parameter could make the troubleshooting easier and more user friendly.

Therefore I recommend you display a simple error instead of running every test and reporting their failure.

[philpep]

I agree, this must be fixed