USN-4720-2: Apport vulnerabilities

USN-4720-1 fixed several vulnerabilities in Apport. This update provides
the corresponding update for Ubuntu 14.04 ESM.

Original advisory details:

Itai Greenhut discovered that Apport incorrectly parsed certain files in
the /proc filesystem. A local attacker could use this issue to escalate
privileges and run arbitrary code. (CVE-2021-25682, CVE-2021-25683)

Itai Greenhut discovered that Apport incorrectly handled opening certain
special files. A local attacker could possibly use this issue to cause
Apport to hang, resulting in a denial of service. (CVE-2021-25684)