cmd/addr2line: use testenv.Command instead of exec.Command in tests

cmd/addr2line: use testenv.Command instead of exec.Command in tests

testenv.Command sets a default based on the test\'s deadline
and sends SIGQUIT (where supported) in case of a hang.

Change-Id: I6710d9866c16610310347d50be1c0916c2976e87
Reviewed-on: https://go-review.googlesource.com/c/go/+/450712
Reviewed-by: Ian Lance Taylor <iant@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Auto-Submit: Bryan Mills <bcmills@google.com>
Run-TryBot: Bryan Mills <bcmills@google.com>