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/docker/tasks/docker-setup-debian.yml

@@ -3,4 +3,3 @@
     state: present
     # Note: add docker-registry when available
     name: docker.io,python-docker,netcat-openbsd,nginx
-

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

@@ -20,4 +20,3 @@
 #- include: registry-tests.yml
   # Add other distributions as the proper packages become available
 #  when: ansible_distribution in ['Fedora']
-

test/integration/targets/docker/tasks/registry-tests.yml

@@ -103,12 +103,12 @@
 - name: Setup nginx with a user/password
   copy:
     src: docker-registry.htpasswd
-    dest:  /etc/nginx/docker-registry.htpasswd
+    dest: /etc/nginx/docker-registry.htpasswd
 
 - name: Setup nginx with a config file
   copy:
     src: nginx-docker-registry.conf
-    dest:  /etc/nginx/conf.d/nginx-docker-registry.conf
+    dest: /etc/nginx/conf.d/nginx-docker-registry.conf
 
 - name: Setup nginx docker cert
   copy:
@@ -186,4 +186,3 @@
     line: "127.0.0.1  dockertest.ansible.com"
     dest: /etc/hosts
     state: absent
-