The actual command that executes is

/usr/bin/python /usr/bin/ubuntu-vm-builder vmw6 xenial -v --arch i386 --domain localdomain --hostname vm-6858 --mem 512 --mirror http://mirrors.mit.edu/ubuntu/ --tmpfs 4096 --components main,universe,multiverse --addpkg linux-image-generic --addpkg build-essential --addpkg ubuntu-standard --addpkg openssh-server --addpkg libacl1-dev --addpkg python --addpkg vim --addpkg emacs --addpkg curl --addpkg libssl-dev --addpkg netcat --addpkg execstack --addpkg python-sqlalchemy --addpkg python-setuptools --addpkg python-flask --addpkg python-lxml --addpkg xvfb --addpkg valgrind --addpkg firefox --addpkg git --addpkg phantomjs --addpkg python-pysqlite2 --addpkg slimit --addpkg open-vm-tools --addpkg autoconf --addpkg dos2unix --addpkg python3.5-venv --addpkg pkg-config --addpkg libfuse-dev --addpkg libffi-dev --addpkg python3.5-dev --addpkg libattr1-dev --addpkg libssl-dev --addpkg pcregrep --addpkg gdb --addpkg bc --removepkg ubuntu-release-upgrader-core --user httpd --pass 6858 --exec vm-fixup.sh --dest vm-6858

where vm-fixup.sh is a post-processing script that changes a couple config files.

Here's a snippet from the install log:

Setting up libp11-kit0:i386 (0.23.2-5~ubuntu16.04.1) ...
Setting up libtasn1-6:i386 (4.7-3ubuntu0.16.04.1) ...
Setting up libgnutls30:i386 (3.4.10-4ubuntu1.1) ...
Setting up libgnutls-openssl27:i386 (3.4.10-4ubuntu1.1) ...
Setting up lsb-release (9.20160110ubuntu0.2) ...
Setting up sudo (1.8.16-0ubuntu1.2) ...

Configuration file '/etc/sudoers'
 ==> Modified (by you or by a script) since installation.
 ==> Package distributor has shipped an updated version.
   What would you like to do about it ?  Your options are:
    Y or I  : install the package maintainer's version
    N or O  : keep your currently-installed version
      D     : show the differences between the versions
      Z     : start a shell to examine the situation
 The default action is to keep your current version.
*** sudoers (Y/I/N/O/D/Z) [default=N] ? dpkg: error processing package sudo (--configure):
 end of file on stdin at conffile prompt
Setting up kbd (1.15.5-1ubuntu5) ...
Setting up console-setup-linux (1.108ubuntu15.2) ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-1.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-13.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-14.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-15.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-2.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-3.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-4.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-7.inc ...
Installing new version of config file /etc/console-setup/compose.ISO-8859-9.inc ...
Setting up console-setup (1.108ubuntu15.2) ...
Your console font configuration will be updated the next time your system
boots. If you want to update it now, run 'setupcon' from a virtual console.
update-initramfs: deferring update (trigger activated)
Processing triggers for systemd (229-4ubuntu16) ...
Processing triggers for ureadahead (0.100.0-19) ...
Processing triggers for libc-bin (2.23-0ubuntu5) ...
Processing triggers for initramfs-tools (0.122ubuntu8.8) ...
update-initramfs: Generating /boot/initrd.img-4.4.0-59-generic
Errors were encountered while processing:
 sudo
Extracting templates from packages: 100%
W: --force-yes is deprecated, use one of the options starting with --allow instead.
E: Sub-process /usr/bin/dpkg returned an error code (1),