replace stdout/err instead of creating a pipes

replace stdout/stderr of the proxy process with TruncateWriter which will only
writes up to N bytes and then discard the rest. N is set to 2 for stdout, and
1024 for stderr. This allows us to not having to drain the pipes to unblock the
outputs.

Docker-DCO-1.1-Signed-off-by: Daniel, Dao Quang Minh <dqminh89@gmail.com> (github: dqminh)