systemtests: Fix build without Python support

Fix CMake Error: "get_target_property() called with non-existent target"
if Python support is FALSE.

systemtests/CMakeLists.txt

@@ -99,10 +99,13 @@ set(mon_sd_password "mon_sd_password")
 set(python_plugin_module_src_dir ${CMAKE_SOURCE_DIR}/core/src/plugins)
 set(plugindirtmp ${PROJECT_BINARY_DIR}/plugindirtmp)
 set(rscripts ${PROJECT_BINARY_DIR}/scripts)
-get_target_property(fd_plugin_binary_path python-fd BINARY_DIR)
-if(NOT client-only)
-  get_target_property(dir_plugin_binary_path python-dir BINARY_DIR)
-  get_target_property(sd_plugin_binary_path python-sd BINARY_DIR)
+
+if(PYTHONLIBS_FOUND)
+  get_target_property(fd_plugin_binary_path python-fd BINARY_DIR)
+  if(NOT client-only)
+    get_target_property(dir_plugin_binary_path python-dir BINARY_DIR)
+    get_target_property(sd_plugin_binary_path python-sd BINARY_DIR)
+  endif()
 endif()
 
 set(sbindir ${PROJECT_BINARY_DIR}/sbin)