USN-6555-2 xorg-server vulnerabilities

USN-6555-1 fixed several vulnerabilities in X.Org. This update provides the corresponding update for Ubuntu 16.04 LTS and Ubuntu 18.04 LTS. Original advisory details: Jan-Niklas Sohn discovered that the X.Org X Server incorrectly handled XKB button actions. An attacker could possibly use this iss...