Unfortunately, a single simple call to pip does not work on all the
distributions that ceph is built on. In particular, Ubuntu 20.04 and
Ubuntu 22.04 come with pip versions that can not correctly handle
disabling wheels and installing Jinja2 (it tries to use the markupsafe
dependency before it is installed). This can be worked around by using a
virtual env and updating pip before proceeding. However, this is not
enough because CentOS/RHEL 8 uses python 3.6 and there is no version of
pip that supports 3.6 that we can update to that is new enough to  fix
the issue with disabling wheels. The workaround in this case is to
install each dependency one at a time through multiple calls to pip.

Because of this extra complexity is it simpler to eschew the use of a
requirements.txt file in build.py entirely. Thus the zipapp is built
using build.py only. Requirements files for cephadm are for setting up
the tox environments *only*.

For completeness a new option is added that gives the caller control
over when build.py uses a virtualenv or not. Thus the build.py script
requires at least one of: a working pip that handles disabling wheels;
or, a virtualenv (venv) and the ability to update to a working version
of pip. If the list of distros ceph supports (and the python versions
they use) ever becomes simpler/newer some of this complexity could be
removed from the build.py script.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Add tests that cover the four main distros that ceph is built on (in
the ceph infra). These tests should not be run by automation as they
are slow and have special requirements like a working podman.
Instead, these are provided to be run by a dev when build.py is updated.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Add tests that check the generation of the standard systemd unit
for cephadm services. This test ensures that non trivial changes
to the content of these files are noticed.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Add Jinja2 and MarkupSafe dependencies to a requirements.txt style file.
This file tracks the dependencies needed to run the cephadm libs
in the unit test framework. The actual dependencies that get added
to the ziapp are managed by build.py but mirrored here.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Add `-rzipapp-reqs.txt` to the unit tests and mypy environments in
tox.ini, enabling the use of dependencies outside the stdlib.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Add a simple wrapper function for templating from a string to a string.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

The somewhat complex string assembly of the main systemd unit file
for cephadm services can benefit from using a standard templating
approach.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Expand the templating module so that templates can be source from the
python package. Add (more) convenient to use methods.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Copy the current template strings into files under the `templates` dir.
Add a enum for holding the names of known template files.

Signed-off-by: John Mulligan <jmulligan@redhat.com>

Switch off of the embedded template strings to using the recently
added template files.

Signed-off-by: John Mulligan <jmulligan@redhat.com>