Add an option to never resolve parent path when vhd-util query is called

[Wescoeur]

Add the ability to vhd-util to find the parent of a VHD without locally resolving or calling stat on the locator path.
A cmdline option -u (unresolved) is now available to query the parent path without resolution.

Use cases:

• When a special SR driver is used where the parent is not always accessible on the master (DRBD case).
• A copy of a VHD on an external device without parent
• ...

Example:

vhd-util query -u -n /dev/drbd/by-res/xcp-volume-1d86819f-c844-4250-8f3a-df5de9227baa/0 -p
../xcp-volume-56c6ef19-3d87-4838-b5e6-9c534bc1a0cb/0

[benjamreis]

LGTM
@MarkSymsCtx what do you think of this change?
Would that be of interest to you?

[Wescoeur]

@TimSmithCtx @MarkSymsCtx I know you are busy but can you take a look? Thanks! 🙂

[MarkSymsCtx]

It looks like quite a specialised case which may not get a lot of use but you do obviously have a use for it so it looks good to me.

[stormi]

Is something missing to reach the point of merging?