Fix chef-server-ctl backup always returning 1

[ryancragun]

Fixes #534
http://wilson.ci.chef.co/job/chef-server-12-trigger-ad_hoc/721/downstreambuildview/

[stevendanna]

I'm 👍 on just merging; however, if you have a few minutes, here are some things I had questions about:

1. Error output should probably go to standard error rather than standard out.
2. Given our purpose, I think the bare rescue makes sense, but I'd prefer to see it just around foreign code (ChefBackup::Runner). The other code we are wrapping looks to be related to transforming user-input into configuration. If something is wrong with those cases, I think we are going to want something more descriptive than the ruby exception message since it probably means the user has input they need to fix.

[marcparadise]

the way omnibus-ctl works you can just 'return 0' , and above 'return 1'. That will be used as the exit code.

[marcparadise]

@stevendanna to the best of my recollection, all of the omnibus-ctl error output (except wrapped chef runs) go to stdout.

[ryancragun]

@stevendanna All error output now goes through STDERR and we only rescue on the foreign code.
@marcparadise I've seen early returns in omnibus-ctl cause jump exceptions because omnibus-ctl will try and yield a non-existent block, hence the specific exits.

[stevendanna]

Thanks for the updates, 👍 from me. Will merge at EOD if there are no objections