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>

tools/docker-compose.yml

@@ -1,3 +1,4 @@
+---
 version: '2'
 services:
   # Primary AWX Development Container
@@ -48,7 +49,7 @@ services:
     image: postgres:10
     container_name: tools_postgres_1
     ports:
-        - "5432:5432"
+      - "5432:5432"
   memcached:
     image: memcached:alpine
     container_name: tools_memcached_1