buildlet: increase timeout period for client
buildlet: increase timeout period for client

The a1.metal instances take about four minutes to become available
before beginning to boot the Windows ARM64 VM. This means we need
somewhere between five and ten minutes before we can first connect to
the buildlet.

It's possible that other instances are faster to boot, but this is
currently the most economical choice.

For golang/go#42604

Change-Id: Ib76944307c9ad28fd1adca0dc54f3fbeaabfffa0
Reviewed-on: https://go-review.googlesource.com/c/build/+/322654
Trust: Alexander Rakoczy <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@golang.org>
Run-TryBot: Alexander Rakoczy <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@golang.org>
TryBot-Result: Go Bot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>

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