Description of problem:
[RFE]Virt-v2v can convert guests from VMware aVpp

Version-Release number of selected component (if applicable):
virt-v2v-2.0.2-1.el9.x86_64
libguestfs-1.48.0-2.el9.x86_64
guestfs-tools-1.48.0-1.el9.x86_64
libvirt-libs-8.2.0-1.el9.x86_64
qemu-img-6.2.0-12.el9.x86_64
nbdkit-server-1.30.2-1.el9.x86_64
libnbd-1.12.2-1.el9.x86_64

How reproducible:
100%

Steps to Reproduce:
1. Create a vApp for ESXi6.7 host on vsphere client

2. Create a VM under vApp, pls refer to screenshot 'vmware-vapp'

3. Convert the guest from VMware vApp by v2v via vddk

1. virt-v2v -ic vpx://root@10.73.73.141/data/10.73.75.219/vapp-m/?no_verify=1 -it vddk -io vddk-libdir=/home/vddk7.0.3 -io vddk-thumbprint=1F:97:34:5F:B6:C2:BA:66:46:CB:1A:71:76:7D:6B:50:1E:03:00:EA rhel8.5-app -ip /home/passwd
   [ 0.0] Setting up the source: -i libvirt -ic vpx://root@10.73.73.141/data/10.73.75.219/vapp-m/?no_verify=1 -it vddk rhel8.5-app
   virt-v2v: error: exception: libvirt: VIR_ERR_INVALID_ARG: VIR_FROM_ESX:
   invalid argument: Path '/data/10.73.75.219/vapp-m/' ends with an excess
   item

If reporting bugs, run virt-v2v with debugging enabled and include the
complete output:

virt-v2v -v -x [...]

4.Convert the guest from VMware vApp by v2v without vddk

1. virt-v2v -ic vpx://root@10.73.73.141/data/10.73.75.219/vapp-m/?no_verify=1 rhel8.5-app -ip /home/passwd
   [ 0.0] Setting up the source: -i libvirt -ic vpx://root@10.73.73.141/data/10.73.75.219/vapp-m/?no_verify=1 rhel8.5-app
   virt-v2v: error: exception: libvirt: VIR_ERR_INVALID_ARG: VIR_FROM_ESX:
   invalid argument: Path '/data/10.73.75.219/vapp-m/' ends with an excess
   item

If reporting bugs, run virt-v2v with debugging enabled and include the
complete output:

virt-v2v -v -x [...]

5.Convert the guest from VMware vApp by v2v via vmx+ssh
5.1 # virt-v2v -i vmx -it ssh ssh://root@10.73.75.219/vmfs/volumes/datastore6.7/rhel8.5-vapp/rhel8.5-vapp.vmx -ip /home/passwd
[ 1.2] Setting up the source: -i vmx ssh://root@10.73.75.219/vmfs/volumes/datastore6.7/rhel8.5-vapp/rhel8.5-vapp.vmx
(root@10.73.75.219) Password:
(root@10.73.75.219) Password:
[ 12.5] Opening the source
nbdkit: ssh[1]: error: all possible authentication methods failed
virt-v2v: error: libguestfs error: could not create appliance through
libvirt.

Try running qemu directly without libvirt using this environment variable:
export LIBGUESTFS_BACKEND=direct

Original error from libvirt: internal error: process exited while
connecting to monitor: 2022-04-07T11:39:00.407075Z qemu-kvm: -blockdev
{"driver":"nbd","server":

,"node-name":"libvirt-2-storage","cache":

,"auto-read-only":true,"discard":"unmap"}:
Requested export not available [code=1 int1=-1]

If reporting bugs, run virt-v2v with debugging enabled and include the
complete output:

virt-v2v -v -x [...]

5.2 # export LIBGUESTFS_BACKEND=direct

5.3 # virt-v2v -i vmx -it ssh ssh://root@10.73.75.219/vmfs/volumes/datastore6.7/rhel8.5-vapp/rhel8.5-vapp.vmx -ip /home/passwd
[ 0.0] Setting up the source: -i vmx ssh://root@10.73.75.219/vmfs/volumes/datastore6.7/rhel8.5-vapp/rhel8.5-vapp.vmx
(root@10.73.75.219) Password:
(root@10.73.75.219) Password:
[ 10.3] Opening the source
nbdkit: ssh[1]: error: all possible authentication methods failed
virt-v2v: error: libguestfs error: guestfs_launch failed.
This usually means the libguestfs appliance failed to start or crashed.
Do:
export LIBGUESTFS_DEBUG=1 LIBGUESTFS_TRACE=1
and run the command again. For further information, read:
http://libguestfs.org/guestfs-faq.1.html#debugging-libguestfs
You can also run 'libguestfs-test-tool' and post the complete output
into a bug report or message to the libguestfs mailing list.

If reporting bugs, run virt-v2v with debugging enabled and include the
complete output:

virt-v2v -v -x [...]

Expected results:
As above description

Additional info: