Tweak test in ExternalProject_Message to avoid warning related to CMP0054

This commit will avoid warning like this one:

//--------------------
CMake Warning (dev) at CMake/ctkMacroCheckExternalProjectDependency.cmake:345 (if):
  Policy CMP0054 is not set: Only interpret if() arguments as variables or
  keywords when unquoted.  Run "cmake --help-policy CMP0054" for policy
  details.  Use the cmake_policy command to set the policy and suppress this
  warning.

  Quoted variables like "SB_SECOND_PASS" will no longer be dereferenced when
  the policy is set to NEW.  Since the policy is not set the OLD behavior
  will be used.
Call Stack (most recent call first):
  CMake/ctkMacroCheckExternalProjectDependency.cmake:596 (ExternalProject_Message)
  CMakeExternals/Log4Qt.cmake:9 (ExternalProject_Include_Dependencies)
  CMake/ctkMacroCheckExternalProjectDependency.cmake:568 (include)
  CMake/ctkMacroCheckExternalProjectDependency.cmake:614 (ExternalProject_Include_Dependencies)
  CMake/ctkBlockCheckDependencies.cmake:132 (ExternalProject_Include_Dependencies)
  CMakeLists.txt:970 (include)
//--------------------
Update tests setting policy CMP0054 to OLD.

This commit sets the policy to OLD so that older version of CMake (where
both quoted and unquoted if parameter are dereferenced) are tested.