test: zero the page we're using for testing

If we don't do this then the buffering threads will see dodgy state.

Signed-off-by: David Scott <dave.scott@citrix.com>
test: connect to the event channel immediately, before any threads start

Signed-off-by: David Scott <dave.scott@citrix.com>
In_memory_events: replace an int with a nice variant

The variant has options
- Unbound: port has never been bound
- Closed: port has been explicitly closed
- Connected: port is connected somewhere

Signed-off-by: David Scott <dave.scott@citrix.com>