Invoke virt-v2v-in-place on host (5.21-edge) (#538)

From #510

This is required for conversion option `virtio` which failed the tests
for 5.21-edge in canonical/lxd-ci#274.

snapcraft.yaml

@@ -1603,6 +1603,7 @@ parts:
         -not -path "${CRAFT_PRIME}/bin/remote-viewer" \
         -not -path "${CRAFT_PRIME}/bin/snap-query" \
         -not -path "${CRAFT_PRIME}/bin/sshfs" \
+        -not -path "${CRAFT_PRIME}/bin/virt-v2v-in-place" \
         -not -path "${CRAFT_PRIME}/bin/xfs_admin" \
         -not -path "${CRAFT_PRIME}/bin/uefivars.py" \
         -not -path "${CRAFT_PRIME}/bin/lxcfs" \
@@ -1659,3 +1660,4 @@ parts:
       wrappers/editor: bin/
       wrappers/remote-viewer: bin/
       wrappers/sshfs: bin/
+      wrappers/virt-v2v-in-place: bin/

snapcraft/wrappers/virt-v2v-in-place

@@ -0,0 +1,14 @@
+#!/bin/sh
+
+CMD="virt-v2v-in-place"
+
+unset XDG_RUNTIME_DIR
+unset LD_LIBRARY_PATH
+
+export PATH="/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
+
+if [ "$(id -u)" = "0" ]; then
+    exec nsenter -t 1 -m "${CMD}" "$@"
+fi
+
+exec unshare -U -r --root="/var/lib/snapd/hostfs/" "${CMD}" "$@"