why python 3.6 when I define python2 as executable

I am trying to install the latest daily package but during the cmake command I got some strange warnings

here the cmake command:
cmake -DUSE_QT5=ON -DPYTHON_EXECUTABLE=/usr/bin/python2 -DCMAKE_VERBOSE_MAKEFILE=ON -Wno-dev -Wno-deprecated -Wno-int-in-bool-context -DENABLE_LBMFLOW=OFF -DENABLE_TWOPHASEFLOW=OFF -DENABLE_PFVFLOW=OFF -DQGLVIEWER_INCLUDE_DIR=/usr/local/include/QGLViewer -DLocal
Boost=1.66.0 -DDEBUG=ON ../trunk

then the warnings messages :
Loop on the following python versions and check available dependencies:3.8;3.7;3.6;3.5;3.4;3.3;3.2;3.1;3.0;2.7;2.6
-- Found PythonInterp: /usr/bin/python3.6 (found version "3.6.5")
Python version 3.6.5 found, try to import dependencies...
CMake Warning at /usr/share/cmake/Modules/FindBoost.cmake:1612 (message):
  No header defined for python-py36; skipping header check
Call Stack (most recent call first):
  cMake/YadePythonHelpers.cmake:62 (FIND_PACKAGE)
  CMakeLists.txt:178 (FIND_PYTHON_PACKAGES)

CMake Warning at /usr/share/cmake/Modules/FindBoost.cmake:1612 (message):
  No header defined for python3-py36; skipping header check
Call Stack (most recent call first):
  cMake/YadePythonHelpers.cmake:62 (FIND_PACKAGE)
  CMakeLists.txt:178 (FIND_PYTHON_PACKAGES)

Failed to import dependencies for Python version 3.6.5. NOT FOUND:libboost-python
-- Found PythonInterp: /usr/bin/python2.7 (found version "2.7.14")
Python version 2.7.14 found, try to import dependencies...
-- Found NumPy: version "1.14.0" /usr/lib64/python2.7/site-packages/numpy/core/include
-- Found IPython: /usr/lib/python2.7/site-packages/IPython
-- Found matplotlib: /usr/lib64/python2.7/site-packages/matplotlib
-- Found pygraphviz: /usr/lib64/python2.7/site-packages/pygraphviz
-- Found Xlib: /usr/lib/python2.7/site-packages/Xlib
-- Found minieigen: /usr/lib64/python2.7/site-packages/minieigen.so
-- Found future: /usr/lib/python2.7/site-packages/future
-- Found past: /usr/lib/python2.7/site-packages/past
-- Found Tkinter: /usr/lib64/python2.7/lib-tk/Tkinter.pyc

why looking at python >2.7 if I have define the executable?

Do I have to insert a new option in the cmake command line?