Fix cosmetic problems in YAML source

This change corrects problems reported by the `yamllint` linter.

Since key duplication problems were removed in 4d48711, this commit
mainly fixes trailing spaces and extra empty lines at beginning/end of
files.

test/integration/targets/async/meta/main.yml

@@ -1,3 +1,2 @@
-dependencies: 
+dependencies:
   - prepare_tests
-

test/integration/targets/async/tasks/main.yml

@@ -57,7 +57,7 @@
         - "'finished' not in async_result or async_result.finished == 0"
 
 - name: test skipped task handling
-  command: /bin/true 
+  command: /bin/true
   async: 15
   poll: 0
   when: False