new: dev: factorize configuration files loading code

bin/compose

@@ -116,23 +116,13 @@ mk_docker_run_options() {
     ##
 
     if [ -z "$DISABLE_SYSTEM_CONFIG_FILE" ]; then
-        if [ -r /etc/default/charm ]; then
-            docker_run_opts+=("-v" "/etc/default/charm:/etc/default/charm:ro")
-            . /etc/default/charm
-        fi
-
         ## XXXvlab: should provide YML config opportunities in possible parent dirs ?
         ##  userdir ? and global /etc/compose.yml ?
-        for cfgfile in /etc/compose.conf /etc/compose.local.conf \
-                                         /etc/default/compose /etc/compose/local.conf; do
+        for cfgfile in "${compose_config_files[@]}"; do
             [ -e "$cfgfile" ] || continue
             docker_run_opts+=("-v" "$cfgfile:$cfgfile:ro")
             . "$cfgfile"
         done
-        for cfgfile in /etc/default/datastore; do
-            [ -e "$cfgfile" ] || continue
-            docker_run_opts+=("-v" "$cfgfile:$cfgfile:ro")
-        done
     else
         docker_run_opts+=("-e" "DISABLE_SYSTEM_CONFIG_FILE=$DISABLE_SYSTEM_CONFIG_FILE")
     fi
@@ -220,6 +210,16 @@ mk_docker_run_options() {
 run() {
     local os docker_run_opts
 
+    ## Order matters, files get to override vars
+    compose_config_files=(
+        /etc/default/charm
+        /etc/default/datastore
+        /etc/compose.conf
+        /etc/compose.local.conf
+        /etc/default/compose
+        /etc/compose/local.conf
+    )
+
     os=$(get_os)
     case "$os" in
         linux)