support separate rickshaw-validate, rickshaw-build, and rickshaw-exec

[atheurer]

The crucible run to support the split of rickshaw-run. This will probably start out as a new crucible command, crucible run-job <one-json-file> or something similar, to allow a transition to the new process. The new process will only work with the one-json file. Most likely this will also support crucible validate and crucible-build, not to be typically used by end-users, but available for debugging or users who would like to step through the validate, build, exec stages manually.