[omaha-client] Finish renaming attempts_to_successful_check metric

This patch reenables the newly renamed metrics
"attempts_to_successful_check".

Test: This adds tests to the omaha-client binary to make sure this metric
are sent to cobalt.

Change-Id: I199a8a96f85c55f80593e556907feaa60f8934c4
Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/450859
Commit-Queue: Erick Tryzelaar <etryzelaar@google.com>
Reviewed-by: Aaron Wood <aaronwood@google.com>
Reviewed-by: Sen Jiang <senj@google.com>
Testability-Review: Olivia Nordquist <nolivia@google.com>