Grid auto register

If a grid hub was restarted, then SelendroidStandaloneServer will re-register itself again.

Commit details:
  a task created for self registration - first check grid if the node already registered, and re-register if not.
  then the task is scheduled for execution (recurrence is configured via -registerCycle argument) 

A nice feature that I found useful when having a farm of selendroid-servers. :-)