There were previously no tests around Dashboard serialization to
protobuf, so this patch adds coverage for that. Also, the `go-cmp`
package has been introduced to replace our usage of `reflect.DeepEqual`
going forward because it has better comparison features that make it
more stable across Go versions and produces nice diffs in tests when
they fail, reducing the need for debug lines and manual inspection.
Edd Robinson
Chris Goller
Tim Raymond