Be more verbose on errors

[goetzc]

Some errors like on login falure should show the actual shell error given by appcenter CLI, as not all errors are related to an incorrect token.

Other reasons for an error to occur could be that the CLI applications is not installed or not in PATH, using an older or newer versions of the CLI working differently, etc. As codepush_login is probably the first step to be run, it should be as descriptive as possible (but not showing the API token value or truncating it) when an error occurs to simplify debugging.