dashboard: extend perf builder timeout
dashboard: extend perf builder timeout

The benchmarks in the perf builder may take several hours to complete.
Extend the VM deletion timeout so that they stick around long enough to
complete benchmarking.

For golang/go#49207.

Change-Id: I3e9d2a1df657406ef0f80b9c0cb713df3b716ca8
Reviewed-on: https://go-review.googlesource.com/c/build/+/378336
Trust: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>
Run-TryBot: Michael Pratt <e7f1edc6d5aa9f6c8c377425db8f1a5816cbbb88@google.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Reviewed-by: Alex Rakoczy <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@golang.org>
Reviewed-by: Carlos Amedee <ab5e2bca84933118bbc9d48ffaccce3bac4eeb64@golang.org>

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