utils._RunCmdPipe: fix poller timeout usage

This patch makes a simple timeout test (e.g. testTimeoutKill) go from
13K poll syscalls to just 6. The code didn't take into account that
RunningTimeout talks in seconds while the poller object expects
milliseconds.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: René Nussbaumer <rn@google.com>