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/elastic/docker-compose.logstash-link-cluster.yml

@@ -1,3 +1,4 @@
+---
 version: '2'
 services:
   # Tower Development Cluster
@@ -9,4 +10,4 @@ services:
       - logstash
   tower_3:
     links:
-      - logstash
+      - logstash