Fixed java tests build

- disabled xfeature2d dependency for java wrappers
- fixed java wrappers build after cmake rerun
- disabled opencv_ml tests temporarily
- fixed Imgproc usage in java tests

cmake/OpenCVDetectPython.cmake

@@ -228,7 +228,7 @@ find_python(3.4 "${MIN_VER_PYTHON3}" PYTHON3_LIBRARY PYTHON3_INCLUDE_DIR
     PYTHON3_NUMPY_INCLUDE_DIRS PYTHON3_NUMPY_VERSION)
 
 # Use Python 2 as default Python interpreter
-if(PYTHON2LIBS_FOUND)
+if(PYTHON2INTERP_FOUND)
     set(PYTHON_DEFAULT_AVAILABLE "TRUE")
     set(PYTHON_DEFAULT_EXECUTABLE "${PYTHON2_EXECUTABLE}")
 endif()