controller: try connection every second

Currently, with 10 tries, it takes up to n(n+1)/2 = 55s before
returning failure.

The default firefox plugin timeout is 45s, passed that time, the plugin
is killed. 10s should be enough in normal usage for the client to setup
the unix socket.

https://bugzilla.redhat.com/show_bug.cgi?id=1073461
controller: return immediately if already connected

Do not try again if the unix socket is already connected, but fail
immediately.

https://bugzilla.redhat.com/show_bug.cgi?id=1073461