Explicitly state FindOpenSCAP cmake so it loads before it's used.

Sometimes it could happen that the OSCAP_VERSION was being used without
being defined first. This makes sure that whenever the variables are
attempted to be used, they are defined.

Fix a problem where cmake would define --schematron option even if the
OSCAP would be greater or equal than 1.3.5.

CMakeLists.txt

@@ -26,6 +26,7 @@ list(APPEND CMAKE_MODULE_PATH "${PROJECT_SOURCE_DIR}/cmake")
 set(CMAKE_INSTALL_LIBDIR "/nowhere")
 include(GNUInstallDirs)
 include(CMakeDependentOption)
+include(FindOpenSCAP)
 include(FindPythonModule)
 include(SSGCommon)