[pve-devel] Add support for multipath-backed direct attached storage

[Dmitry Petuhov]

This patch series adds storage type "mpdirect". Before using it, multipath-tools
package must be installed. After that, multipathd will create /dev/disk/by-id/wwn-0x*
devices, which can be directly attached to VMs via GUI. Partitions are ignored.

I'm not skilled in UI programming, so there's no storage addition via UI. Just add

mpdirect: STORNAME
        content images,rootdir

to storage.cfg.

Because of usage of multipath, this plugin is media-independent:
it was tested with iSCSI, but should also work with FC and SAS/SCSI.

May need manual storage bus rescans to dynamically add new LUNs.