Fix CMake problems in system test

The paths were wrong in the scripts used to run tests. The same problem
was in the CMake files that used CMAKE_SOURCE_DIR instead of
CMAKE_CURRENT_SOURCE_DIR.

Added missing check for BUILD_SYSTEM_TESTS in avrorouter for the
workaround to building without all dependencies present.

server/modules/routing/avrorouter/CMakeLists.txt

@@ -18,7 +18,7 @@ if(AVRO_FOUND AND JANSSON_FOUND)
   if (BUILD_TESTS)
     add_subdirectory(test)
   endif()
-else()
+elseif(NOT BUILD_SYSTEM_TESTS)
   message(FATAL_ERROR "No Avro C or Jansson libraries found, cannot build avrorouter. "
     "Use the -DBUILD_CDC=N  option to `cmake` to disable building of the avrorouter.")
 endif()