Test speedup change to prepare-workspace-git

The child change to prepare-workspace-git explains this in more detail.
We're reducing the number of ansible loops these roles run to reduce
ansible task startup overhead and speed up the role. This change is made
first to the test role so that we can ensure this all works properly
before affecting production zuul installs.

Change-Id: I3d33bb0001e65f449e1026ed323514097088f664

roles/test-prepare-workspace-git/tasks/main.yaml

@@ -1,59 +1,28 @@
-- name: Find locally cached git repos
-  stat:
-    path: "{{ cached_repos_root }}/{{ zj_project.canonical_name }}"
-  with_items: "{{ zuul.projects.values() | list }}"
-  loop_control:
-    loop_var: zj_project
-  register: cached_repos
-
-# We do a bare clone here first so that we skip creating a working copy that
-# will be overwritten later anyway.
-- name: Clone cached repo to workspace
+# Do all the steps in a single shell script. This reduces the number of times
+# ansible must loop over the list of projects which reduces the amount of
+# task startup time we incur.
+- name: Set initial repo states in workspace
   shell: |
-    set -e
-    git clone --bare {{ cached_repos_root }}/{{ zj_project.0.canonical_name }} {{ ansible_user_dir }}/{{ zj_project.0.src_dir }}/.git
-    cd {{ ansible_user_dir }}/{{ zj_project.0.src_dir }}
-    git config --local --bool core.bare false
-  args:
-    creates: "{{ ansible_user_dir }}/{{ zj_project.0.src_dir }}"
-  when: zj_project.1.stat.exists
-  with_together:
-    - "{{ zuul.projects.values() | list }}"
-    - "{{ cached_repos.results }}"
-  loop_control:
-    loop_var: zj_project
-  # ANSIBLE0006: If we use the git module, we get warning
-  # ANSIBLE0004 since we  do not give an explicit version
-  tags:
-    - skip_ansible_lint
-
-- name: Initialize non-cached repos
-  command: "git init {{ ansible_user_dir }}/{{ zj_project.0.src_dir }}"
-  args:
-    creates: "{{ ansible_user_dir }}/{{ zj_project.0.src_dir }}"
-  when: not zj_project.1.stat.exists
-  with_together:
-    - "{{ zuul.projects.values() | list }}"
-    - "{{ cached_repos.results }}"
-  loop_control:
-    loop_var: zj_project
-  # ANSIBLE0006: If we use the git module, we get warning
-  # ANSIBLE0004 since we  do not give an explicit version
-  tags:
-    - skip_ansible_lint
-
-- name: Remove origin from local git repos and replace it by the zuul fake origin
-  # To be idempotent, remove origin only if it's found in the local list.
-  shell: |
-    set -e
+    set -ex
+    if [ -d "{{ cached_repos_root }}/{{ zj_project.canonical_name }}" ] ; then
+        # We do a bare clone here first so that we skip creating a working
+        # copy that will be overwritten later anyway.
+        git clone --bare {{ cached_repos_root }}/{{ zj_project.canonical_name }} {{ ansible_user_dir }}/{{ zj_project.src_dir }}/.git
+        cd {{ ansible_user_dir }}/{{ zj_project.src_dir }}
+        git config --local --bool core.bare false
+    else
+        git init {{ ansible_user_dir }}/{{ zj_project.src_dir }}
+    fi
+    cd {{ ansible_user_dir }}/{{ zj_project.src_dir }}
     git remote -v | grep origin && git remote rm origin || true
     git remote add origin file:///dev/null
   args:
-    chdir: "{{ ansible_user_dir }}/{{ zj_project.src_dir }}"
+    creates: "{{ ansible_user_dir }}/{{ zj_project.src_dir }}"
   with_items: "{{ zuul.projects.values() | list }}"
   loop_control:
     loop_var: zj_project
-  # ANSIBLE0006: git remote is not supported by ansible module
+  # We're using git in a shell script because it is faster and the module
+  # doesn't support features we need.
   tags:
     - skip_ansible_lint