throw error after all saves are done

[IslandRhythms]

closes #4628

[vkarpov15]

Couple of minor issues but LGTM overall

[vkarpov15]

Why is this pre hook here? Doesn't seem to be necessary. Are you just looking for a way to leave some saves in progress to test?

[IslandRhythms]

I just copied the above test and modified it slightly. I see now that for this test that part is not necessary.

[hasezoey]

dosnt #13544 already (somewhat) address this? because enabling aggregateErrors all errors are returned in the result and all operations are waited until finished?

[vkarpov15]

@hasezoey #13544 addresses a similar issue, but this change applies to cases where aggregateErrors is false. Specifically, this change makes it so that you don't need to add an extra option or change your function signature to get the benefits of #4628. create() still works as usual, it just waits for all documents to finish inserting before throwing.