[TIMOB-17346] fallback to defaults if config.json is unreadable

Implementing Ingo's suggestion 3 on https://jira.appcelerator.org/browse/TIMOB-17346
`lib/config.js` is a library file. It should never directly log output. It should throw an exception, which it already did.

You should simply update the error message that's being thrown to include the "run titanium setup" verbiage. On a side note, we always refer to the Titanium CLI command as "titanium" and never as "ti".

Lastly, this PR does nothing to actually solve the problem. If you run "ti setup", it fails because the config.json is still corrupt.