enforce limitation of postCfg needing to be run on pm1

postConfigure is documented as requireing that you run and configure this for what becomes the pm1 server. However it doesn't enforce this and if you end up performing a multi node seperate install and enter values such that the current server ends up being a um server then the install fails badly. We should either remove the limitation or if this is too tricky, enforce or validate the current server is pm1.