macros/pip: revert to old setuptools way

AArch64 builds fail with "AttributeError: install_layout". This is due
to setuptools issue in Debian:

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1003252

Switching setuptools to use distutils from stdlib makes error go away.

Backports: Xena, Wallaby (this is where it was first reported).
Change-Id: I97102e18e4ec47bca94d17d964936f039580b06b
(cherry picked from commit 497b40f)

Author: hrw

docker/macros.j2

@@ -34,7 +34,7 @@
 
 {% macro install_pip(packages, constraints = true) %}
 {%- if packages is sequence and packages|length > 0 -%}
-    python{{ distro_python_version }} -m pip --no-cache-dir install --upgrade{{ ' ' }}
+    SETUPTOOLS_USE_DISTUTILS=stdlib python{{ distro_python_version }} -m pip --no-cache-dir install --upgrade{{ ' ' }}
     {%- if constraints %}-c /requirements/upper-constraints.txt {% endif -%}
     {{ packages | join(' ') }}
 {%- else -%}