Use SO_REUSEADDR before calling bind() where missing. Fixes #1289.

gns3server/compute/qemu/qemu_vm.py

@@ -894,6 +894,7 @@ class QemuVM(BaseNode):
                         af, socktype, proto, _, sa = res
                         # let the OS find an unused port for the Qemu monitor
                         with socket.socket(af, socktype, proto) as sock:
+                            sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
                             sock.bind(sa)
                             self._monitor = sock.getsockname()[1]
                 except OSError as e: