Rescue from ArgumentError when deserializing YAML

YAML.load expects the job's class to exist already. In development, classes are loaded dynamically but YAML.load does not trigger autoloading, so hitting /retries will blow up. In this event we rescue the ArgumentError, log it, and fall back to the wrapper job class name.
Merge pull request #1761 from quikly/display_class_argument_error

Rescue from ArgumentError when deserializing YAML