virsh: undefine: Rename --delete-snapshots to --delete-storage-volume-snapshots

The old flag name confused some users into thinking it's the correct way
to undefine a VM with libvirt (not storage volume) snapshots.

The correct flag in that case is way less obvious: --snapshots-metadata.

Rename the flag (by adding an alias) to something which will promote
looking up the actual purpose of the flag.
Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NFabiano Fidêncio <fidencio@redhat.com>
ACKed-by: NEric Blake <eblake@redhat.com>

tools/virsh-domain.c

@@ -3617,6 +3617,10 @@ static const vshCmdOptDef opts_undefine[] = {
      .help = N_("remove all associated storage volumes (use with caution)")
     },
     {.name = "delete-snapshots",
+     .type = VSH_OT_ALIAS,
+     .help = "delete-storage-volume-snapshots"
+    },
+    {.name = "delete-storage-volume-snapshots",
      .type = VSH_OT_BOOL,
      .help = N_("delete snapshots associated with volume(s), requires "
                 "--remove-all-storage (must be supported by storage driver)")

tools/virsh.pod

@@ -2896,8 +2896,8 @@ is not available the processes will provide an exit code of 1.
 
 =item B<undefine> I<domain> [I<--managed-save>] [I<--snapshots-metadata>]
 [I<--nvram>] [I<--keep-nvram>]
-[ {I<--storage> B<volumes> | I<--remove-all-storage> [I<--delete-snapshots>]}
-I<--wipe-storage>]
+[ {I<--storage> B<volumes> | I<--remove-all-storage>
+[I<--delete-storage-volume-snapshots>]} I<--wipe-storage>]
 
 Undefine a domain. If the domain is running, this converts it to a
 transient domain, without stopping it. If the domain is inactive,
@@ -2932,7 +2932,8 @@ Example: --storage vda,/path/to/storage.img
 The I<--remove-all-storage> flag specifies that all of the domain's storage
 volumes should be deleted.
 
-The I<--delete-snapshots> flag specifies that any snapshots associated with
+The I<--delete-storage-volume-snapshots> (previously I<--delete-snapshots>)
+flag specifies that any snapshots associated with
 the storage volume should be deleted as well. Requires the
 I<--remove-all-storage> flag to be provided. Not all storage drivers
 support this option, presently only rbd.