joy_teleop: add action server auto-refresh

This allowed to get rid of the obnoxious messages saying that action
XXX was not found when starting the node. Now, it will silently
try to register actions every 2 seconds and only display an error
message when an action was triggered but could not be realized.
Merge pull request #3 from po1/background-retry

[joy_teleop] Add action server auto-refresh