hub: fix event.wait timeout
controller: fix send queue draining again

and this time add comments to explain the intention.
context proxy
app_manager: use context proxy
_CAN_PROXY for network
limit the size of ryu app's event queue

otherwise a queue grows too long and consumes much memory on load.
the size used in this commit (128) is arbitrary.
vsctl test code from yamahata
ovs_vsctl.py: rebase and tweaks
ovs_vsctl.py: print timing info
add a ryuapp to provide python interactive console for debugging
object_proxy: add a method to get backend queue
app_manager: create obj frontends for each app
gre_tunnel: create another obj fe for portset