mkosi: Add --noclean when running rpmbuild

The entire build environment is ephemeral anyway so everything is
cleaned regardless. By specifying --noclean, we make debugging
easier as the rpm build root can be inspected when using --debug-shell.

mkosi.images/system/mkosi.conf.d/10-centos-fedora/mkosi.build.chroot

@@ -48,6 +48,7 @@ rpmbuild \
     --define "__elf_exclude_path ^/usr/lib/systemd/tests/unit-tests/.*$" \
     --define "__script_requires %{nil}" \
     --undefine _lto_cflags \
+    --noclean \
     "pkg/$ID/systemd.spec"
 
 cp "$OUTPUTDIR"/*.rpm "$PACKAGEDIR"

mkosi.images/system/mkosi.conf.d/10-opensuse/mkosi.build.chroot

@@ -49,6 +49,7 @@ build() {
         --define "__os_install_post /usr/lib/rpm/brp-suse %{nil}" \
         --define "__elf_exclude_path ^/usr/lib/systemd/tests/unit-tests/.*$" \
         --define "__script_requires %{nil}" \
+        --noclean \
         "$@" \
         "pkg/$ID/systemd.spec"
 }