This patch adds a serial console proxy. This will be used in order
to expose VM serial ports via TCP sockets.
The named pipe IO workers run in native threads and the serial
proxy uses queues to interact with those workers. For this reason,
the serial proxy will use native threads as well.
This implies that logging cannot be used.
Just as the serial console specification states, only one client
can be connected at a time.
This connection will not be used directly, but via the WebSockets
proxy that may run on the controller, which is also responsible of
performing authentication.
Partially-implements: blueprint hyperv-serial-ports
Change-Id: Ie61994a8af7be26a72388d44844e5c482f960891
cae5cdd1fa