cmd/coordinator: don't snapshot in dev mode
cmd/coordinator: don't snapshot in dev mode

In dev mode, we have no GCS storage client, so attempting to write a
snapshot will panic.

For golang/go#48803

Change-Id: Id37264ebd765f914a55acf2fd18274020850331f
Reviewed-on: https://go-review.googlesource.com/c/build/+/353909
Trust: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>
Run-TryBot: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>

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