Soften a possible cluster search setup fatal

Summary:
Ref T12450. The way that config repair and setup issues interact is kind of complicated, and if cluster.search is invalid we may end up using cluster.search before we repair it.

I poked at things for a bit but wasn't confident I could get it to consistently repair before we use it without doing a big messy change.

The only thing that really matters is whether "type" is valid or not, so just put a slightly softer/more-tailored check in for that.

Test Plan:

• With "type": "elastic", loaded setup issues.
• Before patch: hard fatal.
• After patch: softer fatal with more useful messaging.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T12450

Differential Revision: https://secure.phabricator.com/D17576