In https://github.com/systemd/mkosi/pull/3497, mkosi has started parsing
options passed after the verb as regular mkosi options instead of options
for the invoked command. We adapt to this change by adding '--' as a delimiter
everywhere where required.
With the latest mkosi, mkosi takes care of making sure it is
available within mkosi sandbox so we get rid of all the --preserve-env=
options when we invoke mkosi sandbox with sudo as these are not
required anymore. It also doesn't matter anymore if mkosi is installed
in /usr on the host so we get rid of the documentation around that as
well.
Running some mkosi commands as root and other not can lead to cache
invalidations with the latest version, so make sure we run everything
as root after we've built the tools tree.
zypper has some new rather questionable userspace level permission
checking that blows ups completely when operating as root on an
cache directory owned by a non-root user, so let's build the tools
tree and set up meson as root to avoid the issue.
(https://github.com/openSUSE/libzypp/issues/603)
Also drop a leftover debug message from coverage.yml while we're at
it.
Let's enable usage of a tools tree by default to simplify the setup
for new contributors and save them from having to install or upgrade
a bunch of extra tools to get mkosi working as expected.
Move some config option in the right section, fixes the following warning:
```
mkosi.conf: Setting Credentials should be configured in [Runtime], not [Host].
mkosi.conf: Setting RuntimeBuildSources should be configured in [Runtime], not [Host].
mkosi.conf: Setting RuntimeScratch should be configured in [Runtime], not [Host].
mkosi.conf: Setting QemuSmp should be configured in [Runtime], not [Host].
mkosi.conf: Setting QemuSwtpm should be configured in [Runtime], not [Host].
mkosi.conf: Setting QemuVsock should be configured in [Runtime], not [Host].
mkosi.conf: Setting QemuKvm should be configured in [Runtime], not [Host].
```
