ERP5: fix mariadb initialization when datadir is not a simple directory

The previous way to initialize ~/srv/mariadb relied on /bin/mv, so that
it's atomic, making [template-mysqld-wrapper] idempotent (think of a
crash in the middle mysql_install_db). However, mv only works if
~/srv/mariadb is a simple directory: it fails if it's a symlink,
a mount point, or a subvolume (btrfs).

When using extra storage devices for some data, one may prefer to only
put the data (e.g. ~/srv/mariadb) and not the whole slapos partition.
Then if we want a resilient ERP5 with catalog's datadir on a separate
storage device, the importer script must be able to reinitialize
~/srv/mariadb whatever its type.

software/neoppod/software-common.cfg

@@ -105,15 +105,17 @@ template =
   inline:{% raw %}#!/bin/sh -e
   basedir='${mariadb:location}'
   datadir='{{datadir}}'
-  [ -e "$datadir" ] || {
-    rm -vrf "$datadir.new"
+  marker=$datadir/.slapos_initializing
+  [ -d "$datadir/mysql" ] && [ ! -f "$marker" ] || {
+    find "$datadir/" -mindepth 1 ! -path $marker -delete || mkdir "$datadir"
+    touch "$marker"
     "$basedir/scripts/mysql_install_db" \
       --defaults-file='{{defaults_file}}' \
       --skip-name-resolve \
       --auth-root-authentication-method=normal \
       --basedir="$basedir" --plugin_dir="$basedir/lib/plugin" \
-      --datadir="$datadir.new"
-    mv -v "$datadir.new" "$datadir"
+      --datadir="$datadir"
+    rm "$marker"
   }
   {%- if environ is defined %}
   {%-   for variable in environ.splitlines() %}