Apparmor profile caching

[jdstrand]

@jdstrand

Ubuntu’s apparmor init is patched to understand /var/lib/snapd/apparmor/profiles and will load cache files from /var/cache/apparmor for those profiles (this concept dates back to Touch and snappy v1 (but they of course used different profile directories)). Profile caches for snappy end up there and apparmor init makes sure these are loaded on early boot.

Note this will be problematic for non-Debian/non-Ubuntu systems that (will) use apparmor (eg, openSUSE).