starts/stops in containers

As soon as you start/stop a container, or install/remove apport in the container, apport's init.d/upstart script change the global /proc/sys/kernel/core_pattern and thus influence all other containers and the host.

Only the host should set core_pattern, and with https://code.launchpad.net/~stgraber/apport/pidns-support/+merge/200893 crashes in a container are now properly forwarded to the container's apport.

FIX: http://bazaar.launchpad.net/~ubuntu-core-dev/ubuntu/trusty/apport/ubuntu/revision/2274

SRU TEST CASE (stop):
- Check that apport is currently enabled:
  $ cat /proc/sys/kernel/core_pattern
  |/usr/share/apport/apport %p %s %c

- Start a container (that has apport installed):
  $ sudo lxc-start-ephemeral -o precise

- Stop the container:
  $ sudo poweroff # within the container

- Apport is now disabled globally:
  $ cat /proc/sys/kernel/core_pattern
  core

  With the fixed apport, /proc/sys/kernel/core_pattern should never be touched by the container.

SRU TEST CASE (start):
- Stop apport globally:
  $ sudo stop apport
  $ cat /proc/sys/kernel/core_pattern
   core

- Start a container (that has apport installed):
  $ sudo lxc-start-ephemeral -o precise

- Apport is now globally enabled:
  $ cat /proc/sys/kernel/core_pattern
  |/usr/share/apport/apport %p %s %c

  With the fixed apport, /proc/sys/kernel/core_pattern should never be touched by the container.

SRU TEST CASE (regression test):

- Starting/stopping apport manually should still work. After booting, apport should be enabled:
  $ cat /proc/sys/kernel/core_pattern
  |/usr/share/apport/apport %p %s %c
  $ sudo stop apport
  $ cat /proc/sys/kernel/core_pattern
   core
  $ sudo start apport
  $ cat /proc/sys/kernel/core_pattern
  |/usr/share/apport/apport %p %s %c

REGRESSION POTENTIAL: In releases < trusty, apport would not work in containers at all, as the kernel calls the host's apport; before https://code.launchpad.net/~stgraber/apport/pidns-support/+merge/200893, Apport did not forward crashes that happened in a container to the container's apport, so for precise there is no regresssion potential.