squash! zope4py2: fix usage of _Z2HOST

_Z2HOST / _Z2PORT no longer exist in Zope4, something was added in
component/egg-patch/Zope/0001-OFS-XMLExportImport.patch in SlapOS
software release, but we never had a strong need to patch there, we
were doing this so that Testing.ZopeTestCase.utils.makerequest creates
a REQUEST to this host:port, but now that Zope's startZServer no longer,
the REQUEST created by Testing.ZopeTestCase.base.app is always to
nohost:80, so we need to rewrap the app in request to our host:port.