qa_crowbarsetup: check for empty IP addr
qa_crowbarsetup: un-inline code that runs on controller

also mark such functions with oncontroller_ prefix
qa_crowbarsetup: split out addfloatingip function

this fixes reboot tests, which were broken by
commit ba984dee8ff1281dd3d60705673f12e20d41207f
    qa_crowbarsetup: cleanup floating IPs