[Issue-380] Throw exception if log_dir is defined but doesn't exists

tests/Resources/invalid-log.yml

@@ -0,0 +1,27 @@
+magephp:
+    log_dir: /no-temp
+    environments:
+        production:
+            user: app
+            branch: master
+            host_path: /var/www/myapp
+            releases: 4
+            exclude:
+                - ./var/cache/*
+                - ./var/log/*
+                - ./web/app_dev.php
+            hosts:
+                - webserver1
+                - webserver2
+                - webserver3
+            pre-deploy:
+                - git/update
+                - composer/install
+                - composer/dump-autoload
+            on-deploy:
+                - symfony/cache-warmup: { env: 'dev' }
+                - symfony/assets-install: { env: 'dev' }
+                - symfony/assetic-dump: { env: 'dev' }
+            on-release:
+            post-release:
+            post-deploy: