Don't send command output too fast.

Changes done in eows package of xds-common now allow to accumulate command output during a period
of time (eg. 500ms) or up to the end of a line.
Usage of this feature is mandatory to avoid to post to
much buffers in websocket and consequently flood client (eg. web-browser)

Signed-off-by: Sebastien Douheret <sebastien.douheret@iot.bzh>