Work around the ambiguity of the vApp power off action through the REST api.
Executing powerOff from the API is only powering off the VMs but the vApp
is still deployed (and put in a partia;lly running state).
As a result, the vApp is not considered powered off by operations which
need the vApp in that state (e.g. recompose).
Implement power off action by undeploying the vApp.
No need to handle power off exceptions.
Correct sprintf syntax.