cgroups: handle non-existent isolcpus file
cgroups: handle non-existent isolcpus file

If the file "/sys/devices/system/cpu/isolated" doesn't exist, we can't just
simply bail. We still need to check whether we need to copy the parents cpu
settings.

Signed-off-by: Christian Brauner <48455ab3070520a2d174545c7239d6d0fabd9a83@canonical.com>

Xeno22/lxcfs,Xeno22/lxcfs