Revisit error handling for JSON parsing errors

[justingaylor]

It's important to know what failed to parse in JSON. However, including that information in the exception message might be too long (for large JSON). Might be better to log this information.

Also, may be important to consider not logging sensitive data, such as SSH keys material.

Per discussion here: https://github.com/rightscale/attributor/pull/26/files#r6810501

[gampleman]

This is a duplicate of https://github.com/rightscale/attributor/issues/29.