Pin Gaudi version on lhcb-head and lhcb-run2-patches

Pin the Gaudi version to the latest available v36r16 in lhcb-head and lhcb-run2-patches as discussed at PAC today. /cc @cattanem

I have also disabled the build of Gaudi since v36r16 is already on cvmfs.

Slots that were so far using Gaudi/HEAD remain unchanged.

To be reviewed if this makes sense for lhcb-gaussino and lhcb-gaussino-fastsim /cc @mimazure