Multi-host checks - checking for identical key/file & value

We might want/need the ability to perform checks that can use information from multiple hosts. For example:

• A "dynamic" check for all hosts being on the same version
  • We can do a static check easily – by the version of each individual node to a static/supplied version we can spot nodes that are not equal to that version. But we can currently not collect all versions from all nodes and see if they are all the same value – regardless of what that value is.
• Sometimes a known issue might have conditions that spans multiple hosts (this scenario now has its own issue, #132)
  • For example, "only if Gitaly is running on a certain OS version and the Rails nodes have config option xyz" – currently the best we could do is make a check for the most specific subcondition and tell people to manually check for the other condition.

Is this something we anticipate to need (often)? Is it worth designing a solution – soon, or for v2 / v3?