Support dry-run mode

[ash2k]

Perhaps a REST endpoint that accepts POST with a Bundle object and returns detailed explanation of what is going to happen if this object is stored:

• Which objects are going to be created
• Which objects are going to be updated
  • A diff for each one?
• Which object are going to be deleted
• What status will the Bundle have
  • Not a final status, but the one after the very first pass. This is to catch issues with the Bundle object itself.
• What else?

[wryun]

AFAIK this can't give us a proper dry-run because we have to assume any object with a reference to a changed object is tainted, whereas on actual execution this might not be true (e.g. if I change my db parameters, and my compute has a dependency on the db, it looks like compute might be changed... but then we run it and we find that the hostname is unaltered).

Hmm, although secrets may obscure this mechanism. Interesting. Don't properly understand how service catalog handles bindings (e.g. when should bindings be regenerated?). Need to discuss.