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/samples/test_include.yml

@@ -22,4 +22,3 @@
   #handlers:
   #- name: foo
   #  include: include.yml a="this is a handler"
-