WIP: [SPI-1448] motif is actually built only for mac

I am not sure if this contribution makes sense in general, if it is correct and if the problem described below cannot be solved in a different way.

For normal build nodes with CentOS or SLC motif has to be present in the system and then it doesn't appear in the dependencies of packages (e.g. Geant4). The problem appeared on cvmfs upload machine which lacked the library, but actually it should ignore it as it is only meant to unpack ready tarfiles and make a view. By hiding motif it should disappear always from dependencies and packages are forced to always rely on the system version. Because cvmfs lacked motif, it started to build it with lcgcmake and it changed the hash of Geant4 forcing it to be built on cvmfs machine as well.