Install systemd-python from distribution package

CentOS 8 support start to fail because of an issue [1]
compiling systemd python binding modules.
Let install it from distribution packages as documented by
python-systemd project Web page [2]

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1862714
[2] https://github.com/systemd/python-systemd

Closes-Bug: #1908386
Change-Id: Ic7cfd72ce1b875e75b1cdbdd44a902b25d51abb8

doc/source/systemd.rst

@@ -196,31 +196,6 @@ See the `remote-pdb`_ home page for more options.
 
 .. _`remote-pdb`: https://pypi.org/project/remote-pdb/
 
-Known Issues
-============
-
-Be careful about systemd python libraries. There are 3 of them on
-pypi, and they are all very different. They unfortunately all install
-into the ``systemd`` namespace, which can cause some issues.
-
-- ``systemd-python`` - this is the upstream maintained library, it has
-  a version number like systemd itself (currently ``234``). This is
-  the one you want.
-- ``systemd`` - a python 3 only library, not what you want.
-- ``python-systemd`` - another library you don't want. Installing it
-  on a system will break ansible's ability to run. The package has now
-  been renamed to ``cysystemd``, which avoids the namespace collision.
-
-
-If we were using user units, the ``[Service]`` - ``Group=`` parameter
-doesn't seem to work with user units, even though the documentation
-says that it should. This means that we will need to do an explicit
-``/usr/bin/sg``. This has the downside of making the SYSLOG_IDENTIFIER
-be ``sg``. We can explicitly set that with ``SyslogIdentifier=``, but
-it's really unfortunate that we're going to need this work
-around. This is currently not a problem because we're only using
-system units.
-
 Future Work
 ===========
 

files/debs/general

@@ -28,6 +28,7 @@ pkg-config
 psmisc
 python3-dev
 python3-pip
+python3-systemd
 python3-venv
 tar
 tcpdump

files/rpms-suse/general

@@ -20,10 +20,10 @@ openssl
 pcre-devel # python-pcre
 postgresql-devel  # psycopg2
 psmisc
+python3-systemd
 python-cmd2 # dist:opensuse-12.3
 python-devel  # pyOpenSSL
 python-xml
-systemd-devel # for systemd-python
 tar
 tcpdump
 unzip

files/rpms/general

@@ -25,8 +25,8 @@ postgresql-devel  # psycopg2
 psmisc
 python3-devel
 python3-pip
+python3-systemd
 redhat-rpm-config # missing dep for gcc hardening flags, see rhbz#1217376
-systemd-devel # for systemd-python
 tar
 tcpdump
 unzip

stack.sh

@@ -761,7 +761,6 @@ fixup_all
 # Install subunit for the subunit output stream
 pip_install -U os-testr
 
-pip_install_gr systemd-python
 # the default rate limit of 1000 messages / 30 seconds is not
 # sufficient given how verbose our logging is.
 iniset -sudo /etc/systemd/journald.conf "Journal" "RateLimitBurst" "0"