fix: allow ssh login for nova user in nova image (#1852)

Login should be enabled for nova resizing or migrating between hypervisors 1.
diff --git a/zuul.d/container-images/nova.yaml b/zuul.d/container-images/nova.yaml
index a74080a..fcb1382 100644
--- a/zuul.d/container-images/nova.yaml
+++ b/zuul.d/container-images/nova.yaml
@@ -51,6 +51,7 @@
           build_args:
             - "RELEASE={{ zuul.branch | replace('stable/', '') }}"
             - PROJECT=nova
+            - SHELL=/bin/bash
           tags:
             - "{{ zuul.branch | replace('stable/', '') }}"
     files: &container_image_files