inline streamlined version of build_i18n & intltool into our setup.py

I found the layers and layers of other tools just confusing.

"python3 setup.py build" generates an identical (apart from timestamp)
POT file and an identical build directory before and after this change.

setup.py

@@ -22,18 +22,48 @@ subiquity
 Ubuntu Server Installer
 """
 
-from setuptools import setup, find_packages
-
+import distutils.cmd
+import distutils.command.build
+import glob
 import os
+import subprocess
 import sys
 
-setup_kwargs = {}
-# dpkg build uses build and install, tox uses sdist
-if 'SUBIQUITY_NO_I18N' not in os.environ:
-    from DistUtilsExtra.command import build_extra
-    from DistUtilsExtra.command import build_i18n
-    setup_kwargs['cmdclass'] = {'build': build_extra.build_extra,
-                                'build_i18n': build_i18n.build_i18n}
+from setuptools import setup, find_packages
+
+
+class build(distutils.command.build.build):
+
+    def run(self):
+        super().run()
+        data_files = self.distribution.data_files
+
+        with open('po/POTFILES.in') as in_fp:
+            with open('po/POTFILES.in.tmp', 'w') as out_fp:
+                for line in in_fp:
+                    if line.startswith('['):
+                        continue
+                    out_fp.write('../' + line)
+
+        subprocess.run([
+            'xgettext',
+            '--directory=.',
+            '--add-comments',
+            '--from-code=UTF-8',
+            '--output=subiquity.pot',
+            '--files-from=POTFILES.in.tmp',
+            ], cwd="po")
+        os.unlink('po/POTFILES.in.tmp')
+
+        for po_file in glob.glob("po/*.po"):
+            lang = os.path.basename(po_file[:-3])
+            mo_dir = os.path.join("build", "mo", lang, "LC_MESSAGES")
+            mo_file = os.path.join(mo_dir, "subiquity.mo")
+            if not os.path.exists(mo_dir):
+                os.makedirs(mo_dir)
+            subprocess.run(["msgfmt", po_file, "-o", mo_file])
+            targetpath = os.path.join("share/locale", lang, "LC_MESSAGES")
+            data_files.append((targetpath, (mo_file,)))
 
 
 with open(os.path.join(os.path.dirname(__file__),
@@ -43,6 +73,7 @@ with open(os.path.join(os.path.dirname(__file__),
     exec('\n'.join(lines), ns)
     version = ns['__version__']
 
+
 if sys.argv[-1] == 'clean':
     print("Cleaning up ...")
     os.system('rm -rf subiquity.egg-info build dist')
@@ -75,4 +106,5 @@ setup(name='subiquity',
           ],
       },
       data_files=[],
-      **setup_kwargs)
+      cmdclass={'build': build},
+      )

snapcraft.yaml

@@ -68,7 +68,6 @@ parts:
       - libsystemd-dev
       - lsb-release
       - pkg-config
-      - python3-distutils-extra
       - python3-urwid
     stage-packages:
       - cloud-init
@@ -76,7 +75,6 @@ parts:
       - iso-codes
       - lsb-release
       - python3-bson
-      - python3-distutils-extra
       - python3-urwid
       - python3-requests
       - python3-requests-unixsocket