runtime/pprof: retry vmmap invocation if it failed due to a reported temporary resour...

runtime/pprof: retry vmmap invocation if it failed due to a reported temporary resource shortage

As per #62352 the invocation of vmmap may fail (very rarely) due to
a temporary lack of resources on the test runner machine. This PR
allows for retrying the invocation a fixed number of times before
giving up. This is because we suspect the failure is due to
sensible to retry.

Fixes: #62352
Change-Id: I51aa66b949753d8127cc307181b6ef32e91d5b05
Reviewed-on: https://go-review.googlesource.com/c/go/+/545935
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>
Reviewed-by: Bryan Mills <bcmills@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Cherry Mui <cherryyz@google.com>