Put the local socket in non-blocking mode in the async client

_connect_unix left the socket blocking, while _connect_tls sets a zero
timeout, so every loop.sock_recv and sock_sendall against the local
socket ran the blocking call inline and stalled the whole event loop.
nodeconsole --video showed this most clearly: a power action opens its
own session, so the tiles stopped refreshing and keystrokes went
unhandled until the BMC finished.

asyncio only enforces this in debug mode, where the client failed
outright with ValueError: the socket must be non-blocking.  The
descriptor passing retries in asynctlvdata also assume a non-blocking
socket, since they wait for BlockingIOError.

confluent_client/confluent/asynclient.py

@@ -396,6 +396,7 @@ class Command(object):
         self.connection = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
         self.connection.setsockopt(socket.SOL_SOCKET, SO_PASSCRED, 1)
         self.connection.connect(self.serverloc)
+        self.connection.setblocking(False)
 
     async def _connect_tls(self):
         server, port = _parseserver(self.serverloc)