[pve-devel] pve-container: add support for mountpoint part 2

[Alexandre Derumier]

Changelog:

- attach loop device after activate storage/volume.
- don't write mount.entry for blockdev mounpoints (lxc can't manage blockdev in mount.entry)
- use pve conf for mount hook instead instead lxc-conf
- add post stop hook to do the vm_stop_cleanup
- dettach loopdev in vm_stop_clenaup 



Improve me : add support for devices passthrough
mp0:/dev/sdX   (without storeid)