Stop using deprecated CMake code

Use the FindPython module instead of the deprecated FindPythonInterp
module. Require a reasonably new version of CMake instead of 2.8.2
due to deprecated compatibility with CMake older than 3.5.

Fixes: #13073

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 2.8.12)
+cmake_minimum_required(VERSION 3.16)
 
 # Strictly speaking in-source will work but will be very messy so it is not supported.
 if("${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_BINARY_DIR}")
@@ -131,11 +131,8 @@ else()
 endif()
 message(STATUS "PYTHONPATH: $ENV{PYTHONPATH}")
 
-# Setting Python_ADDITIONAL_VERSIONS before calling PythonInterp can influence the priority of
-# python executables in a scenario where multiple versions are present.
-set(Python_ADDITIONAL_VERSIONS 3 2)
 # Required Packages
-find_package(PythonInterp REQUIRED)
+find_package(Python REQUIRED)
 find_package(OpenSCAP REQUIRED)
 
 find_program(ANSIBLE_LINT_EXECUTABLE NAMES ansible-lint)
@@ -230,7 +227,7 @@ configure_file("${CMAKE_SOURCE_DIR}/build_config.yml.in" "${CMAKE_BINARY_DIR}/bu
 message(STATUS " ")
 message(STATUS "Summary of Python Tools and Modules:")
 # Required Python Tools
-message(STATUS "python: ${PYTHON_EXECUTABLE} (version: ${PYTHON_VERSION_STRING})")
+message(STATUS "python: ${Python_EXECUTABLE} (version: ${Python_VERSION})")
 message(STATUS "python yaml module: ${PY_YAML}")
 message(STATUS "python jinja2 module: ${PY_JINJA2}")
 # Optional Python Tools

cmake/FindPythonModule.cmake

@@ -14,7 +14,7 @@ function(find_python_module module)
             set(PY_${module}_FIND_REQUIRED TRUE)
         endif()
         if($ENV{SSG_USE_PIP_PACKAGES})
-            execute_process(COMMAND "${PYTHON_EXECUTABLE}" "-c"
+            execute_process(COMMAND "${Python_EXECUTABLE}" "-c"
                 "import platform; print(''.join('python'+platform.python_version()[:-2]))"
                 RESULT_VARIABLE _python_version_status
                 OUTPUT_VARIABLE _python_version
@@ -26,7 +26,7 @@ function(find_python_module module)
         endif()
         # A module's location is usually a directory, but for binary modules
         # it's a .so file.
-        execute_process(COMMAND "${PYTHON_EXECUTABLE}" "-c"
+        execute_process(COMMAND "${Python_EXECUTABLE}" "-c"
             "import re, ${module}; print(re.compile('/__init__.py.*').sub('',${module}.__file__))"
             RESULT_VARIABLE _${module}_status
             OUTPUT_VARIABLE _${module}_location