stop sending keepalives to loggregator

this appears to be done via websocket ping/pongs instead, which
gorilla/websocket automatically does for us

Signed-off-by: Simon Leung <leungs@us.ibm.com>
add test for docker nsync flow

rebuilt dockerapp to use $VCAP_APPLICATION so that we can reuse it here

Signed-off-by: Simon Leung <leungs@us.ibm.com>
remove prebuilt dockerapp binary

Signed-off-by: Simon Leung <leungs@us.ibm.com>