Handle tags in infra docs publishing

We publish docs for infra projects on tags for projects like bindep.
Previously the afs publishing role for this assumed zuul.branch was
always going to be present but it isn't when operating on a tag in the
release pipeline. Update the conditionals to properly handle the case of
zuul.tag being present and zuul.branch missing.

Change-Id: Iee2a7f43a92a63c1943755ff46a03c94f096d6bc

roles/prepare-infra-docs-for-afs/tasks/main.yaml

@@ -2,19 +2,26 @@
   set_fact:
     doc_build_dir: "{{ zuul_work_dir }}/{{ sphinx_build_dir }}"
 
-- name: Write marker text
+- name: Write branch marker text
   copy:
     dest: "{{ doc_build_dir }}/html/.root-marker"
     content: "Project: {{ zuul.project.name }} Branch: {{ zuul.branch }} Build: {{ zuul.build }} Revision: {{ zuul.ref }}"
+  when: "zuul.branch is defined"
+
+- name: Write tag marker text
+  copy:
+    dest: "{{ doc_build_dir }}/html/.root-marker"
+    content: "Project: {{ zuul.project.name }} Tag: {{ zuul.tag }} Build: {{ zuul.build }} Revision: {{ zuul.ref }}"
+  when: "zuul.tag is defined"
 
 - name: Process tagged build
   include: tagged.yaml
-  when: "zuul.branch != 'master' and zuul.tag is defined"
+  when: "zuul.tag is defined"
 
 - name: Process stable branch build
   include: stable.yaml
-  when: "'stable' in zuul.branch and zuul.tag is not defined"
+  when: "zuul.branch is defined and 'stable' in zuul.branch and zuul.tag is not defined"
 
 - name: Process branch build
   include: branch.yaml
-  when: "zuul.branch != 'master' and 'stable' not in zuul.branch and zuul.tag is not defined"
+  when: "zuul.branch is defined and zuul.branch != 'master' and 'stable' not in zuul.branch and zuul.tag is not defined"

roles/prepare-infra-docs-for-afs/tasks/tagged.yaml

@@ -14,5 +14,5 @@
     path: "{{ doc_build_dir }}/html/{{ zuul.tag | dirname }}"
     state: directory
 
-- name: Move html to branch location
+- name: Move html to tag location
   command: "mv {{ doc_build_dir }}/tmp {{ doc_build_dir }}/html/{{ zuul.tag }}"