cmd/coordinator: extend macOS builder health check coverage
cmd/coordinator: extend macOS builder health check coverage

Use reverseHostChecker, which handles when a builder restarts between
builds and reconnects quickly—without displaying a fatal error during
that time. Delete the simple hostTypeChecker which does not do that.

This CL tries to implement a temporary fix to make the health check
more useful while the work on adding more builders (and making them
sustainable) is still underway.

For golang/go#49149.

Change-Id: If5fe39b0c7a854a8bcce3095e356d7d2b8faec7e
Reviewed-on: https://go-review.googlesource.com/c/build/+/399041
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Auto-Submit: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Reviewed-by: Alex Rakoczy <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@google.com>

golang/build,golang/build,golang/build,golang/build