Bug 576945: StreamsProxy needs to be closed after app exit

Capture and forward all output from application by closing the
StreamsProxy after the graceful exit timeout.

Contributed by STMicroelectronics

Change-Id: I139e414ee0b617085cbe66df3d788e73f1b50e78
Signed-off-by: Torbjörn SVENSSON <torbjorn.svensson@st.com>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.debug/+/187134
Tested-by: Platform Bot <platform-bot@eclipse.org>
Reviewed-by: Jonah Graham <jonah@kichwacoders.com>