LXC: create a bind mount for sysfs when enable userns but disable netns
LXC: create a bind mount for sysfs when enable userns but disable netns

kernel commit 7dc5dbc879bd0779924b5132a48b731a0bc04a1e
forbid us doing a fresh mount for sysfs
when enable userns but disable netns.
This patch will create a bind mount in this senario.

Signed-off-by: Chen Hanxiao <818f8a165c25fa146ecad28e2ef3e3fb996fa364@cn.fujitsu.com>

fabianfreyer/libvirt,eskultety/libvirt,shugaoye/libvirt,shugaoye/libvirt,crobinso/libvirt,libvirt/libvirt,nertpinx/libvirt,rlaager/libvirt,crobinso/libvirt,jardasgit/libvirt,datto/libvirt,nertpinx/libvirt,olafhering/libvirt,andreabolognani/libvirt,shugaoye/libvirt,andreabolognani/libvirt,olafhering/libvirt,crobinso/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,zippy2/libvirt,olafhering/libvirt,libvirt/libvirt,eskultety/libvirt,zippy2/libvirt,zippy2/libvirt,nertpinx/libvirt,libvirt/libvirt,elmarco/libvirt,andreabolognani/libvirt,nertpinx/libvirt,shugaoye/libvirt,VenkatDatta/libvirt,VenkatDatta/libvirt,eskultety/libvirt,jardasgit/libvirt,rlaager/libvirt,agx/libvirt,datto/libvirt,agx/libvirt,shugaoye/libvirt,taget/libvirt,elmarco/libvirt,taget/libvirt,fabianfreyer/libvirt,eskultety/libvirt,datto/libvirt,elmarco/libvirt,eskultety/libvirt,rlaager/libvirt,agx/libvirt,datto/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,taget/libvirt,agx/libvirt,zippy2/libvirt,datto/libvirt,taget/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,jfehlig/libvirt,rlaager/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,agx/libvirt,crobinso/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,taget/libvirt,jardasgit/libvirt,elmarco/libvirt,libvirt/libvirt,olafhering/libvirt,jardasgit/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,elmarco/libvirt,rlaager/libvirt,nertpinx/libvirt