cmd/coordinator: triple writeSnapshot timeout for reverse builders
cmd/coordinator: triple writeSnapshot timeout for reverse builders

This timeout is meant to be an upper bound, and some reverse builders
have been observed to need a bit over 5 minutes to finish the upload.
Give them more time and update the comment to describe the 2022 state.

Also log how many bytes they've managed to copy before failing.

Updates golang/go#52235.
Updates golang/go#49149.

Change-Id: I20f850620f0aa8126968862f2ad9a096fa32ce03
Reviewed-on: https://go-review.googlesource.com/c/build/+/398697
Trust: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>
Reviewed-by: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>
Trust: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Auto-Submit: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Reviewed-by: Heschi Kreinick <e89ab2b172855aa0ad01c40c4d8a3535a61ac68a@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

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