change the volume_support default to False

With volume_support enabled, trove will require that new instances use
swift. It works fine without swift though and I suppose we want to avoid
an unneeded dependency on swift.
Than there are multiple places where this is the case. So we should think about clean code guidelines like give proper method names or add option hashes. But this looks for me as a pure ruby developer simply wrong to initialize a variable just for nothing.