Make LXC fail verification if cgroup is not mounted
Make LXC fail verification if cgroup is not mounted

Since LXC now relies on cgroup memory limits to enforce memory, let's
make hypervisor verification (and thus cluster-verify) return errors
when the cgroup filesystem is not mounted.

Signed-off-by: Iustin Pop <acf83a5274f31a43af6b914614365999469c1a31@google.com>
Reviewed-by: Michael Hanselmann <68b67885ff74281219b4a4be33cc20fd45078d7c@google.com>

leshchevds/ganeti,dimara/ganeti,ganeti/ganeti,andir/ganeti,mbakke/ganeti,apyrgio/snf-ganeti,bitemyapp/ganeti,yiannist/ganeti,apyrgio/ganeti,apyrgio/snf-ganeti,ganeti/ganeti,grnet/snf-ganeti,onponomarev/ganeti,mbakke/ganeti,andir/ganeti,leshchevds/ganeti,ganeti-github-testing/ganeti-test-1,grnet/snf-ganeti,leshchevds/ganeti,apyrgio/ganeti,yiannist/ganeti,dimara/ganeti,ganeti/ganeti,andir/ganeti,yiannist/ganeti,ganeti-github-testing/ganeti-test-1,mbakke/ganeti,bitemyapp/ganeti,onponomarev/ganeti