Fix “There is no suitable CSPRNG installed on your system” in Plesk

After updating paragonie/random_compat you may get this error. This is caused because version 2.0 stopped using OpenSSL and now it uses /dev/urandom which may not be readable by your PHP configuration. This is fixed adding /dev/urandom to your open_base configuration in "Websites & Domains -> PHP Settings -> open_basedir":

Ref: http://forum.odin.com/threads/how-to-change-php-open_basedir-in-plesk-10-4-4.259102/
https://forum.owncloud.org/viewtopic.php?t=34286
https://github.com/paragonie/random_compat/issues/99