[Python] Use CPython libraries over distuils

As distutils and Easy Install are deprecated

c.f.:
* https://setuptools.pypa.io/en/stable/deprecated/distutils-legacy.html
* https://setuptools.pypa.io/en/stable/deprecated/easy_install.html

it is perferable to convert use of distutils to either use existing CPython
libraries or use setuptool's versions of them. This patch applies

* distutils.spawn.find_executable -> shutil.which

Henry Schreiner pointed out that shutil.which (added in Python 3.3) is perferable
to setuptools._distutils.spawn.find_executable.

This patch was meant to also change:

* distutils.setup -> setuptools.setup
* distutils.sysconfig -> CPython's sysconfig

but it seems that these are still required given the current state of the build
and will need to be revised in a later PR.

The change

distutils.core.Extension -> setuptools.Extension

could be applied in:

* bindings/python/setup_pypi.py
* bindings/python/setup_standalone.py

but isn't as these files are obsolete and should be removed.

Co-authored-by: Henry Schreiner <henry.fredrick.schreiner@cern.ch>

packaging/wheel/setup.py

@@ -3,6 +3,13 @@
 from setuptools.command.sdist import sdist
 from wheel.bdist_wheel import bdist_wheel
 
+# shutil.which was added in Python 3.3
+# c.f. https://docs.python.org/3/library/shutil.html#shutil.which
+try:
+    from shutil import which
+except ImportError:
+    from distutils.spawn import find_executable as which
+
 import subprocess
 import sys
 import getpass
@@ -27,11 +34,9 @@ def get_version_from_file():
 
 def binary_exists(name):
     """Check whether `name` is on PATH."""
-    from distutils.spawn import find_executable
-    return find_executable(name) is not None
+    return which(name) is not None
 
 def check_cmake3(path):
-    from distutils.spawn import find_executable
     args = (path, "--version")
     popen = subprocess.Popen(args, stdout=subprocess.PIPE)
     popen.wait()
@@ -42,12 +47,11 @@ def check_cmake3(path):
 
 def cmake_exists():
     """Check whether CMAKE is on PATH."""
-    from distutils.spawn import find_executable
-    path = find_executable('cmake')
+    path = which('cmake')
     if path is not None:
         if check_cmake3(path): return True, path
-    path = find_executable('cmake3')
-    return path is not None, path 
+    path = which('cmake3')
+    return path is not None, path
 
 def is_rhel7():
     """check if we are running on rhel7 platform"""
@@ -78,9 +82,8 @@ def has_cxx14():
 
 # def python_dependency_name( py_version_short, py_version_nodot ):
 #     """ find the name of python dependency """
-#     from distutils.spawn import find_executable
 #     # this is the path to default python
-#     path = find_executable( 'python' )
+#     path = which( 'python' )
 #     from os.path import realpath
 #     # this is the real default python after resolving symlinks
 #     real = realpath(path)