feat(config): validate config before applying

nginx/config.sls

     - context:
         config: {{ nginx.server.config|json(sort_keys=False) }}
 {% endif %}
+{% if nginx.check_config_before_apply %}
+    - check_cmd: /usr/sbin/nginx -t -c
+{% endif %}

nginx/map.jinja

     'install_from_ppa': False,
     'install_from_repo': False,
     'install_from_phusionpassenger': False,
+    'check_config_before_apply': False,
     'ppa_version': 'stable',
     'source_version': '1.10.0',
     'source_hash': '8ed647c3dd65bc4ced03b0e0f6bf9e633eff6b01bac772bcf97077d58bc2be4d',

pillar.example

   source_version: '1.10.0'
   source_hash: ''
 
+  # Check the configuration before applying:
+  # To prevent applying a configuration that might break nginx, set this
+  # parameter to true so the configuration is checked BEFORE applying. If
+  # the check fails, the state will fail and it won't be deployed.
+  # CAVEAT: As the configuration file is created in a temp dir, it can't
+  # have relative references or it will fail to check. You'll need to
+  # specify full paths where required (ie, `include`, `load_module`,
+  # `snippets`, etc.0
+  # Defaults to false
+  check_config_before_apply: false
+
   # These are usually set by grains in map.jinja
   # Typically you can comment these out.
   lookup: