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>

.yamllint

@@ -0,0 +1,12 @@
+---
+ignore: |
+  .tox
+  awx/main/tests/data/inventory/plugins/**
+  # vault files
+  awx/main/tests/data/ansible_utils/playbooks/valid/vault.yml
+  awx/ui/test/e2e/tests/smoke-vars.yml
+
+extends: default
+
+rules:
+  line-length: disable