opensplice_cmake_module: workaround for os x

The filesystem is case insensitive, so it creates an infinite loop until cmake segfaults. This works around this by removing this module's directory from the `CMAKE_MODULE_PATH` before looking for the other module shipped with our opensplice package. I then restore it. I think this is safe since the path will be `<prefix>/share/opensplice_cmake_module/cmake` and so it shouldn't contain any other modules.