Add new job_status module

Provides methods for getting and setting job status. This is necessary
because we used to just use a boolean called 'success'. In order to stop
reporting infrastructure errors as failures, we need more than just a
boolean.

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>
Use new functions provided by job_status

Signed-off-by: Zack Cerza <zack.cerza@inktank.com>