cmd/coordinator: use Request.Context in handleLogs
cmd/coordinator: use Request.Context in handleLogs

CloseNotify has been deprecated in favor of Request.Context.
Start using the newer API to avoid the panic when CloseNotify
gets called too late.

Fixes golang/go#44244.

Change-Id: I1f01c2d42cf6735d1161b977b62a7d982e8a61ea
Reviewed-on: https://go-review.googlesource.com/c/build/+/291769
Trust: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Alexander Rakoczy <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@golang.org>
Reviewed-by: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>

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