add FindUUID.cmake module
look for libuuid in global CMakeLists.txt
FIX: don't repeat 'Found UUID'
link against libuuid in cvmfs/CMakeLists.txt
Refactor: don't repeat link libraries
link against libuuid in test/unittests/CMakeLists.txt
Merge pull request #626 from reneme/fix-cmake_uuid

Fix: CMake Integration for libuuid