Grab json log contents for final post playbook failures

If the final post playbook fails, something has gone wrong with log
uploading, which means it's very hard to debug. Grab the contents of the
json log file, extract the log for the last playbook and add it to the
executor log.

Change-Id: Ia930311e121c350e73e41b20e9b742b2eac9c9f6
diff --git a/tests/fixtures/config/job-output/git/common-config/playbooks/job-output-failure-post.yaml b/tests/fixtures/config/job-output/git/common-config/playbooks/job-output-failure-post.yaml
new file mode 100644
index 0000000..bd46718
--- /dev/null
+++ b/tests/fixtures/config/job-output/git/common-config/playbooks/job-output-failure-post.yaml
@@ -0,0 +1,4 @@
+- hosts: all
+  tasks:
+    - shell: echo "Failure test {{ zuul.executor.src_root }}"
+    - shell: exit 1
diff --git a/tests/fixtures/config/job-output/git/common-config/zuul.yaml b/tests/fixtures/config/job-output/git/common-config/zuul.yaml
index a83f0bc..f182d8d 100644
--- a/tests/fixtures/config/job-output/git/common-config/zuul.yaml
+++ b/tests/fixtures/config/job-output/git/common-config/zuul.yaml
@@ -20,8 +20,19 @@
     parent: base
     name: job-output
 
+- job:
+    name: job-output-failure
+    run: playbooks/job-output
+    post-run: playbooks/job-output-failure-post
+
 - project:
     name: org/project
     check:
       jobs:
         - job-output
+
+- project:
+    name: org/project2
+    check:
+      jobs:
+        - job-output-failure
diff --git a/tests/fixtures/config/job-output/git/org_project2/README b/tests/fixtures/config/job-output/git/org_project2/README
new file mode 100644
index 0000000..9daeafb
--- /dev/null
+++ b/tests/fixtures/config/job-output/git/org_project2/README
@@ -0,0 +1 @@
+test
diff --git a/tests/fixtures/config/job-output/main.yaml b/tests/fixtures/config/job-output/main.yaml
index 208e274..14b382f 100644
--- a/tests/fixtures/config/job-output/main.yaml
+++ b/tests/fixtures/config/job-output/main.yaml
@@ -6,3 +6,4 @@
           - common-config
         untrusted-projects:
           - org/project
+          - org/project2