runtime: fix threshold calculation of TestPhysicalMemoryUtilization
runtime: fix threshold calculation of TestPhysicalMemoryUtilization

Variable 'procs' used to calculate the threshold of overuse in
TestPhysicalMemoryUtilization should be updated if GOMAXPROCS
gets changed, otherwise the threshold could be a large number,
making the test meaningless.

Change-Id: I876cbf11457529f56bae77af1e35f4538a721f95
Reviewed-on: https://go-review.googlesource.com/c/go/+/210297
Run-TryBot: Michael Knyszek <4473450dc5c88f06e1fb787f303d7805ec2aee65@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Michael Knyszek <4473450dc5c88f06e1fb787f303d7805ec2aee65@google.com>

akutz/go,nawawi/go,golang/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,nawawi/go,cloudflare/go,nawawi/go,golang/go,CAFxX/go,golang/go,nawawi/go,nawawi/go,akutz/go,cloudflare/go,nawawi/go,golang/go,cloudflare/go,CAFxX/go,CAFxX/go,cloudflare/go,CAFxX/go,akutz/go,cloudflare/go,golang/go,akutz/go,CAFxX/go,CAFxX/go,cloudflare/go,akutz/go,golang/go,golang/go,cloudflare/go,akutz/go,nawawi/go,akutz/go,akutz/go