Wrapper for _fullClone(). In the case of failure, if clobberOnFailure
           is set to True remove the build directory and try a full clone again.

def _fullCloneOrFallback(self):
        """Wrapper for _fullClone(). In the case of failure, if clobberOnFailure
           is set to True remove the build directory and try a full clone again.
        """

        res = yield self._fullClone()
        if res != RC_SUCCESS:
            if not self.clobberOnFailure:
                raise buildstep.BuildStepFailed()
            res = yield self.clobber()
        return res