Skip app install if already available

[alessiopiazza]

One of the common issue that we see when provisioning it that some apps (eg: iTerm, Slack..) may already available be on the host and this causes a failure in the playbook. We should check for the app presence before trying to install it

[paolomainardi]

As we are using brew through ansible, it shouldn’t happen.

[paolomainardi]

They should be overwrited and/or updated.

[paolomainardi]

done