Fix yamllint issues and make it blocker

All yamllint issues in yaml files have been fixed except line-length rule
which is excluded. tox.ini is updated in order not to ignore yamllint issues
so if yamllint fails, the change will get verified-1 and will be blocked from
merging. yamllint configuration file, .yamllint, is also created to configure
what is enforced.

As a summary, most frequently occurring issues that are fixed are below.
- truthy value: must be true/false and not yes/no
- indentation: blocks are incorrectly indented mostly
- braces: extra spaces after opening and before closing curly braces are not good
- colons: extra spaces after colons - should be single
- missing document start
- comments: there should be a space after hash

Change-Id: I0d1341f2639585228b1ae8fd6ee073e5cae53604
diff --git a/playbooks/roles/configure-targethosts/tasks/install-packages.yml b/playbooks/roles/configure-targethosts/tasks/install-packages.yml
index 3d5beb5..0bcd3fc 100644
--- a/playbooks/roles/configure-targethosts/tasks/install-packages.yml
+++ b/playbooks/roles/configure-targethosts/tasks/install-packages.yml
@@ -22,31 +22,31 @@
 
 - name: Config docker proxy
   block:
-  - name: Check that /etc/systemd/system/docker.service.d exists
-    stat:
-      path: "/etc/systemd/system/docker.service.d"
-    register: dir_stats
+    - name: Check that /etc/systemd/system/docker.service.d exists
+      stat:
+        path: "/etc/systemd/system/docker.service.d"
+      register: dir_stats
 
-  - name: Create /etc/systemd/system/docker.service.d if not exists
-    file:
-      path: "/etc/systemd/system/docker.service.d"
-      state: directory
-    when: not dir_stats.stat.exists
+    - name: Create /etc/systemd/system/docker.service.d if not exists
+      file:
+        path: "/etc/systemd/system/docker.service.d"
+        state: directory
+      when: not dir_stats.stat.exists
 
-  - name: Create proxy conf file under /etc/systemd/system/docker.service.d/
-    file:
-      path: "/etc/systemd/system/docker.service.d/http-proxy.conf"
-      state: touch
+    - name: Create proxy conf file under /etc/systemd/system/docker.service.d/
+      file:
+        path: "/etc/systemd/system/docker.service.d/http-proxy.conf"
+        state: touch
 
-  - name: Config docker proxy in http-proxy.conf
-    blockinfile:
-      dest: "/etc/systemd/system/docker.service.d/http-proxy.conf"
-      block: |
-        [Service]
-        Environment="HTTP_PROXY={{ idf.proxy_settings.http_proxy }}"
-        Environment="HTTPS_PROXY={{ idf.proxy_settings.https_proxy }}"
-        Environment="NO_PROXY={{ idf.proxy_settings.no_proxy }}"
+    - name: Config docker proxy in http-proxy.conf
+      blockinfile:
+        dest: "/etc/systemd/system/docker.service.d/http-proxy.conf"
+        block: |
+          [Service]
+          Environment="HTTP_PROXY={{ idf.proxy_settings.http_proxy }}"
+          Environment="HTTPS_PROXY={{ idf.proxy_settings.https_proxy }}"
+          Environment="NO_PROXY={{ idf.proxy_settings.no_proxy }}"
   when:
-      idf.proxy_settings is defined
+    idf.proxy_settings is defined
 
 # vim: set ts=2 sw=2 expandtab: