yamllint: Make all files in awx pass yamllint

This commit updates all files that weren't passing yamllint for them to
pass.

A new yamllint target has been added. One can run `tox -e yamllint` or
`yamllint -s .` locally to ensure yaml files are still passing.

This check will be enabled in the CI so it can get on every new
contributions, and prevent merging non-compliant code.

Signed-off-by: Yanis Guenane <yguenane@redhat.com>

installer/build.yml

@@ -3,5 +3,5 @@
   hosts: all
   gather_facts: false
   roles:
-    - { role: image_build }
-    - { role: image_push, when: "docker_registry is defined" }
+    - {role: image_build}
+    - {role: image_push, when: "docker_registry is defined"}