Init system support for toposerver

There is a new component toposerver in 7.6, used by Roxie for keeping track of node locations when autoscaling.

hpcc-init should be updated to ensure that any toposerver processes will be started up properly. Also the relevant config process changes will be needed so that toposerver processes can be added to the environment, and the generation of RoxieTopology.xml should be updated so that Roxie automatically knows the location of the toposervers.

We can assume that all toposervers in the environment are equivalent if it simplifies things.