报错内容：
Data directory (/var/www/html/owncloud/data) not writable by ownCloud
Permissions can usually be fixed by giving the webserver write access to the ownCloud directory
这个官网的设置教程是这么写的：
The owner of your webserver must own the apps/, data/ and config/ directories in your ownCloud install. You can do this by running the following command for the apps, data and config directories:chown -R www-data:www-data /path/to/your/owncloud/install/data
这个config和apps两个文件夹都没有问题，就这个data文件夹有问题
