Improve logging around listening services

I wanted to bring listen_tcp into line with listen_ssl in terms of returning a
list of ports, and wanted to check that was a safe thing to do - hence the
logging in `refresh_certificate`.

Also, pull the 'Synapse now listening' message up to homeserver.py, because it
was being duplicated everywhere else.

synapse/app/_base.py

@@ -162,21 +162,23 @@ def listen_tcp(bind_addresses, port, factory, reactor=reactor, backlog=50):
     Create a TCP socket for a port and several addresses
 
     Returns:
-        list (empty)
+        list of twisted.internet.tcp.Port listening for TLS connections
     """
+    r = []
     for address in bind_addresses:
         try:
-            reactor.listenTCP(
-                port,
-                factory,
-                backlog,
-                address
+            r.append(
+                reactor.listenTCP(
+                    port,
+                    factory,
+                    backlog,
+                    address
+                )
             )
         except error.CannotListenError as e:
             check_bind_error(e, address, bind_addresses)
 
-    logger.info("Synapse now listening on TCP port %d", port)
-    return []
+    return r
 
 
 def listen_ssl(
@@ -203,7 +205,6 @@ def listen_ssl(
         except error.CannotListenError as e:
             check_bind_error(e, address, bind_addresses)
 
-    logger.info("Synapse now listening on port %d (TLS)", port)
     return r
 
 
@@ -229,6 +230,10 @@ def refresh_certificate(hs):
             # requests. This factory attribute is public but missing from
             # Twisted's documentation.
             if isinstance(i.factory, TLSMemoryBIOFactory):
+                addr = i.getHost()
+                logger.info(
+                    "Replacing TLS context factory on [%s]:%i", addr.host, addr.port,
+                )
                 # We want to replace TLS factories with a new one, with the new
                 # TLS configuration. We do this by reaching in and pulling out
                 # the wrappedFactory, and then re-wrapping it.

synapse/app/homeserver.py

@@ -121,7 +121,7 @@ class SynapseHomeServer(HomeServer):
         root_resource = create_resource_tree(resources, root_resource)
 
         if tls:
-            return listen_ssl(
+            ports = listen_ssl(
                 bind_addresses,
                 port,
                 SynapseSite(
@@ -134,9 +134,10 @@ class SynapseHomeServer(HomeServer):
                 self.tls_server_context_factory,
                 reactor=self.get_reactor(),
             )
+            logger.info("Synapse now listening on TCP port %d (TLS)", port)
 
         else:
-            return listen_tcp(
+            ports = listen_tcp(
                 bind_addresses,
                 port,
                 SynapseSite(
@@ -148,6 +149,9 @@ class SynapseHomeServer(HomeServer):
                 ),
                 reactor=self.get_reactor(),
             )
+            logger.info("Synapse now listening on TCP port %d", port)
+
+        return ports
 
     def _configure_named_resource(self, name, compress=False):
         """Build a resource map for a named resource