USN-4171-5: Apport regression

USN-4171-1 fixed vulnerabilities in Apport. This caused a regression in
autopkgtest and python2 compatibility. This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

Kevin Backhouse discovered Apport would read its user-controlled settings
file as the root user. This could be used by a local attacker to possibly
crash Apport or have other unspecified consequences. (CVE-2019-11481)

Sander Bos discovered a race-condition in Apport during core dump
creation. This could be used by a local attacker to generate a crash report
for a privileged process that is readable by an unprivileged user.
(CVE-2019-11482)

Sander Bos discovered Apport mishandled crash dumps originating from
containers. This could be used by a local attacker to generate a crash
report for a privileged process that is readable by an unprivileged user.
(CVE-2019-11483)

Sander Bos discovered Apport mishandled lock-file creation. This could be
used by a local attacker to cause a denial of service against Apport.
(CVE-2019-11485)

Kevin Backhouse discovered Apport read various process-specific files with
elevated privileges during crash dump generation. This could could be used
by a local attacker to generate a crash report for a privileged process
that is readable by an unprivileged user. (CVE-2019-15790)