runtime: include stderr when objdump fails

runtime: include stderr when objdump fails

If objdump panics, we want the panic included in the test log.

Change-Id: I6a6a636c13c5ba08acaa1c6c8714541a8e91542b
Reviewed-on: https://go-review.googlesource.com/c/go/+/704338
Reviewed-by: Florian Lehner <lehner.florian86@gmail.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
Reviewed-by: Michael Knyszek <mknyszek@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>