Failure in getPage callback causes the verification grid to hard fail

[hudson-newey]

Because the getPage callback is user-supplied, we cannot guarantee that it will not be falkey

However, if the getPage callback does throw an error, we currently hard-fail and the verification grid will be left in an unknown (sometimes unresponsive) partial state.

We should catch getPage errors, raise them, and retry to fetch after a certain timeout or a page of results has been verified.