CI: Don't download Cirros or IPA in seed jobs

We build IPA images and a deployment image in the seed jobs, so we don't
need to download Cirros or IPA images. Also, these downloads depend on
external resources which may make jobs less reliable.

For seed upgrade jobs, disable IPA and deployment image downloads.

Change-Id: Ib59c8bc2d8938eca18c943bb2e66ed185152a739

playbooks/kayobe-seed-base/bifrost-overrides.yml.j2

----
-# Don't build an IPA deployment image, instead download upstream images.
-create_ipa_image: false
-download_ipa: true
-
-# Don't build a disk image. It takes time and can be unreliable.
-use_cirros: true

playbooks/kayobe-seed-base/pre.yml

@@ -30,11 +30,6 @@
         path: "{{ kayobe_config_src_dir }}/etc/kayobe/kolla/config/bifrost"
         state: "directory"
 
-    - name: Ensure bifrost overrides file exists
-      template:
-        src: bifrost-overrides.yml.j2
-        dest: "{{ kayobe_config_src_dir }}/etc/kayobe/kolla/config/bifrost/bifrost.yml"
-
     - name: Ensure kayobe is installed
       shell:
         cmd: dev/install.sh &> {{ logs_dir }}/ansible/install

playbooks/kayobe-seed-upgrade-base/bifrost-overrides.yml.j2

 ---
-# Don't build an IPA deployment image, instead download upstream images.
+# Don't build an IPA deployment image.
 create_ipa_image: false
-download_ipa: true
+download_ipa: false
 
 # Don't build a disk image. It takes time and can be unreliable.
-use_cirros: true
+create_image_via_dib: false