Gateway: Cancelling the connect operation fails and leaks the port forwarding

[vrubezhny]

When connecting to a DevSpaces Workspace using a Join Link it's almost impossible to cancel the operation.

Also, after a try to cancel it, in most cases the port forward created gets leaked and makes the following try to fail with the "Port in use" error.

[vrubezhny]

After releasing redhat-developer/devspaces-gateway-plugin#188 the issue becomes less critical, as a different port number is to be selected for the next connection try instead of the "locked" one.