Pull underlying capabilities up to 00-multus.conf

Using Python, we analyze the content of the master plugin configuration,
and we integrate any capabilities from the chained plugins declaration.
This way, we can for example have the  portMapping capability ( declared
for the `portmap` chained plugin) that will be included in the top-level
CNI configuration file, `00-multus.conf`, and the container runtime will
correctly send `runtimeConfig` attributes based on the capabilities.
The script is compatbile with Python 2 and Python 3, it could be a bit
shorter if I used only Python 3 syntax.

Fixes #544

Signed-off-by: <clement.nussbaumer@swisscom.com>

images/entrypoint.sh

@@ -302,6 +302,25 @@ if [ "$MULTUS_CONF_FILE" == "auto" ]; then
         MASTER_PLUGIN_NET_NAME="multus-cni-network"
       fi
 
+      capabilities_python_filter_tmpfile=$(mktemp)
+      cat << EOF > $capabilities_python_filter_tmpfile
+import json,sys
+conf = json.load(sys.stdin)
+capabilities = {}
+for capa in [p['capabilities'] for p in conf['plugins'] if 'capabilities' in p]:
+    capabilities.update(capa)
+enabled_capa = {capa:enabled for (capa,enabled) in capabilities.items() if enabled}
+if len(enabled_capa) > 0:
+    print("""\"capabilities\": """ + json.dumps(enabled_capa) + ",")
+else:
+    print("")
+EOF
+
+      NESTED_CAPABILITIES_STRING="$(cat $MULTUS_AUTOCONF_DIR/$MASTER_PLUGIN | \
+            python $capabilities_python_filter_tmpfile)"
+      rm $capabilities_python_filter_tmpfile
+      log "Nested capabilities string: $NESTED_CAPABILITIES_STRING" 
+
       MASTER_PLUGIN_LOCATION=$MULTUS_AUTOCONF_DIR/$MASTER_PLUGIN
       MASTER_PLUGIN_JSON="$(cat $MASTER_PLUGIN_LOCATION)"
       log "Using $MASTER_PLUGIN_LOCATION as a source to generate the Multus configuration"
@@ -311,6 +330,7 @@ if [ "$MULTUS_CONF_FILE" == "auto" ]; then
           "name": "$MASTER_PLUGIN_NET_NAME",
           "type": "multus",
           $ISOLATION_STRING
+          $NESTED_CAPABILITIES_STRING
           $LOG_LEVEL_STRING
           $LOG_FILE_STRING
           $ADDITIONAL_BIN_DIR_STRING