nose: clean up, support Python 3.10. (#8825)

Due to changes in setuptools, we need to run 2to3 ourselves.
While we're at it, lets apply relevant patches from Debian.

https://salsa.debian.org/python-team/packages/nose/

dev-python/nose/patches/debian/docs-sys.path.diff

@@ -0,0 +1,26 @@
+From: Dmitry Shachnev <mitya57@debian.org>
+Date: Sat, 8 Feb 2020 12:26:00 +0300
+Subject: Use correct sys.path when building docs
+
+The parent directory contains Python 2 nose, however we need the
+Python 3 version, which we will pass via PYTHONPATH.
+---
+ doc/conf.py | 5 +----
+ 1 file changed, 1 insertion(+), 4 deletions(-)
+
+diff --git a/doc/conf.py b/doc/conf.py
+index 34ea147..ac7f0cb 100644
+--- a/doc/conf.py
++++ b/doc/conf.py
+@@ -20,10 +20,7 @@ import sys, os
+ # is relative to the documentation root, use os.path.abspath to make it
+ # absolute, like shown here.
+ 
+-# need to be brutal because of easy_install's pth hacks:
+-sys.path.insert(0,
+-    os.path.abspath(os.path.join(os.path.dirname(__file__), '..')))
+-sys.path.insert(0, os.path.abspath('.'))
++sys.path[0] = os.path.abspath('.')
+ 
+ from nose import __versioninfo__ as nose_version
+ nose_version = tuple(str(x) for x in nose_version)