Comment 1 for bug 1505783

I updated the backport to take the latest SRU too.

On top of that I did the following (documented in changelog) changes to the packaging:
   * Add a versioned build-dependency on trusty-backports' libseccomp-dev.
   * Add a versioned build-dependency on trusty-backports' libcgmanager-dev.
   * Add a versioned depends for liblxc1 on trusty-backports' cgmanager.
   * Add a versioned recommends for liblxc1 on trusty-backports' cgmanager.

LXC supports building with old versions of those libraries so that's why there's no versioned dependency on those in the archive. But for the backport, we'd like to use the backported version of those since they add useful features and optimizations.