title: Cmake seems not to use the Python interpreter it confirms it uses
body: <p>I have the following CMakeLists.txt file, which is instructed to use Python 4.4</p>
  
  <pre><code>cmake_minimum_required(VERSION 3.2 FATAL_ERROR)
  set(CMAKE_MODULE_PATH ${CMAKE_MODULE_PATH} "${CMAKE_SOURCE_DIR}/../cmake/")
  
  project(aConfigd VERSION 1.0)
  string(TOLOWER aConfigd project_id)
  
  find_package(PythonInterp 3.4 REQUIRED)
  
  include(FindPythonInterp)
  set(PYTHON ${PYTHON_EXECUTABLE})
  message(STATUS "\${PYTHON_EXECUTABLE} == ${PYTHON_EXECUTABLE}")
  set(pkgdatadir /usr/share/configd)
  set(configdir /etc/amy)
  set(SONARCONFIGID_SOURCE_DIR etc/configd)
  set(SRC_DIR configd/src/)
  
  include(common)
  #        "${SRC_DIR}/systemd_client.py"
  #        "${SRC_DIR}/amyconfig_service.py"
          "${SRC_DIR}/__init__.py"
          "${SRC_DIR}/main.py"
          "${SRC_DIR}/application.py"
          DESTINATION ${pkgdatadir}/configd/
  )
  
  #general
  set(CPACK_PACKAGE_NAME "a-config")
  set(CPACK_PACKAGE_DESCRIPTION_SUMMARY "a-config-manager")
  set(CPACK_PACKAGE_DESCRIPTION "a-config-manager")
  
  # redhat
  set(CPACK_RPM_EXCLUDE_FROM_AUTO_FILELIST_ADDITION 
        /etc/amy
        )
  
  include(cpack)
  </code></pre>
  
  <p>Indeed, it confirms that <code>${PYTHON_EXECUTABLE} == /usr/bin/python3.4</code> (see 4th line below):</p>
  
  <pre><code>$ make clean ; cmake -DCMAKE_BUILD_TYPE=Release -DSHORT_VERSION=NO -DCUSTOMER=NO .. ;  make -j12 ; make package
  -- Found PythonInterp: /usr/bin/python3.4 (found suitable version "3.4.5", minimum required is "3.4") 
  -- Found PythonInterp: /usr/bin/python3.4 (found version "3.4.5") 
  -- ${PYTHON_EXECUTABLE} == /usr/bin/python3.4
  -- Build Type: Release
  -- Detected distribution: rhel fedora
  -- Detected aConfigd version: 2.3.0-3030-gf7733cf659
  -- Detected distribution: rhel fedora
  -- Configuring done
  -- Generating done
  -- Build files have been written to: /local/raid0/git/amy/aConfig/build
  Run CPack packaging tool...
  CPack: Create package using RPM
  CPack: Install projects
  CPack: - Run preinstall target for: aConfigd
  CPack: - Install project: aConfigd
  CPack: Create package
  CPackRPM:Warning: CPACK_SET_DESTDIR is set (=ON) while requesting a relocatable package (CPACK_RPM_PACKAGE_RELOCATABLE is set): this is not supported, the package won't be relocatable.
  CPackRPM: Will use GENERATED spec file: /local/raid0/git/my/aConfig/build/_CPack_Packages/Linux/RPM/SPECS/a-config.spec
  CPack: - package: /local/raid0/git/my/aConfig/build/a-config-2.3.0-3030-gf7733cf659.el7.my.x86_64.rpm generated.
  $ 
  </code></pre>
  
  <p>However, if I uncomment the <code>"${SRC_DIR}/systemd_client.py"</code> line, I get the error:</p>
  
  <pre><code>Compiling /local/raid0/git/my/aConfig/build/_CPack_Packages/Linux/RPM/a-config-2.3.0-3030-gf7733cf659.el7.my.x86_64/usr/share/configd/configd/systemd_client.py ...
    File "/usr/share/configd/configd/systemd_client.py", line 21
      def __init__(self, systemd_proxy:Gio.DBusProxy):
                                      ^
  SyntaxError: invalid syntax
  </code></pre>
  
  <p><strong>Isn't <code>def __init__(self, systemd_proxy:Gio.DBusProxy): a valid Python 3.4</code> syntax?<br>
  If yes, why does Cmake complains?</strong></p>