[modules/docker] Exception when daemon is not running

When the docker daemon is not running, only the call to
containers.list() actually throws an exception, so move that into the
exception guard.

fixes #608

modules/contrib/docker_ps.py

@@ -33,11 +33,11 @@ class Module(core.module.Module):
         try:
             cli = docker.DockerClient(base_url='unix://var/run/docker.sock')
             cli.ping()
+            self.__info = 'OK - {}'.format(len(cli.containers.list(filters={'status': 'running'})))
         except ConnectionError:
             self.__info = 'daemon off'
         except Exception:
             self.__info = 'n/a'
-        self.__info = 'OK - {}'.format(len(cli.containers.list(filters={'status': 'running'})))
         return self.__info
 
 # vim: tabstop=8 expandtab shiftwidth=4 softtabstop=4