virt-bootstrap fails on virt-builder delete /boot/efi

[stephen322]

After getting around issue #9 by adding read permissions for the kernel, it still fails on Ubuntu 20.04:

$ virt-bootstrap -d virt-builder://ubuntu-20.04 /somedest/
WARNING : All extracted files will be owned by the current unprivileged user.
INFO : Building image
[ 2.9] Downloading: http://builder.libguestfs.org/ubuntu-20.04.xz
[ 3.8] Planning how to build this image
[ 3.8] Uncompressing
[ 7.1] Opening the new disk
[ 9.6] Setting a random seed
virt-builder: warning: random seed could not be set for this type of guest
[ 9.7] Deleting: /dev/*
[ 9.7] Deleting: /boot/*
virt-builder: error: libguestfs error: rm_rf: /boot/efi: rm: cannot remove
'/sysroot/boot/efi': Device or resource busy

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

virt-builder -v -x [...]
Traceback (most recent call last):
File "/usr/local/lib/python3.8/dist-packages/virtBootstrap/sources/virt_builder_source.py", line 96, in unpack
self.build_image(tmp_file.name)
File "/usr/local/lib/python3.8/dist-packages/virtBootstrap/sources/virt_builder_source.py", line 78, in build_image
self.run_builder(cmd)
File "/usr/local/lib/python3.8/dist-packages/virtBootstrap/sources/virt_builder_source.py", line 84, in run_builder
subprocess.check_call(cmd)
File "/usr/lib/python3.8/subprocess.py", line 364, in check_call
raise CalledProcessError(retcode, cmd)
subprocess.CalledProcessError: Command '['virt-builder', 'ubuntu-20.04', '-o', '/tmp/bootstrap__wv95dio', '--no-network', '--delete', '/dev/', '--delete', '/boot/', '--edit', '/etc/fstab:s/^/#/']' returned non-zero exit status 1.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/local/bin/virt-bootstrap", line 11, in
load_entry_point('virt-bootstrap==1.1.1', 'console_scripts', 'virt-bootstrap')()
File "/usr/local/lib/python3.8/dist-packages/virtBootstrap/virt_bootstrap.py", line 349, in main
bootstrap(uri=args.URI,
File "/usr/local/lib/python3.8/dist-packages/virtBootstrap/virt_bootstrap.py", line 164, in bootstrap
source(uri=uri,
File "/usr/local/lib/python3.8/dist-packages/virtBootstrap/sources/virt_builder_source.py", line 154, in unpack
raise Exception("Unknown format:" + self.output_format)
File "/usr/lib/python3.8/tempfile.py", line 631, in exit
self.close()
File "/usr/lib/python3.8/tempfile.py", line 638, in close
self._closer.close()
File "/usr/lib/python3.8/tempfile.py", line 575, in close
unlink(self.name)
FileNotFoundError: [Errno 2] No such file or directory: '/tmp/bootstrap__wv95dio'