Drop root for Magnum

This change ensures commands run in the magnum containers are done as the
'magnum' user rather than root.

Change-Id: I18e2febae98aae6d6fc6c61cc2817442f408cb75
Partially-Implements: blueprint drop-root

docker/magnum/magnum-api/Dockerfile.j2

@@ -14,3 +14,5 @@ COPY extend_start.sh /usr/local/bin/kolla_extend_start
 RUN chmod 755 /usr/local/bin/kolla_extend_start
 
 {{ include_footer }}
+
+USER magnum

docker/magnum/magnum-api/extend_start.sh

@@ -3,6 +3,6 @@
 # Bootstrap and exit if KOLLA_BOOTSTRAP variable is set. This catches all cases
 # of the KOLLA_BOOTSTRAP variable being set, including empty.
 if [[ "${!KOLLA_BOOTSTRAP[@]}" ]]; then
-    sudo -H -u magnum magnum-db-manage upgrade
+    magnum-db-manage upgrade
     exit 0
 fi

docker/magnum/magnum-conductor/Dockerfile.j2

@@ -16,3 +16,5 @@ RUN cd /tmp && curl -L https://github.com/GoogleCloudPlatform/kubernetes/release
 {% endif %}
 
 {{ include_footer }}
+
+USER magnum