Add moby-engine to docker dependencies for debian packages

This change allows nvidia-docker2 to be installed on systems where moby-engine is used instead of docker-ce, docker-ee, or docker.io.

This is limited to Ubuntu and Debian-based systems.

When installing a previous version:

$ sudo apt-get install -y nvidia-docker2=2.10.0-1
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
 nvidia-docker2 : Depends: docker-ce (>= 18.06.0~ce~3-0~ubuntu) but it is not installable or
                           docker-ee (>= 18.06.0~ce~3-0~ubuntu) but it is not installable or
                           docker.io (>= 18.06.0) but it is not going to be installed
E: Unable to correct problems, you have held broken packages.

The generated packages shows:

$ dpkg --info nvidia-docker2_2.11.0~rc.4-1_all.deb
 new Debian package, version 2.0.
 size 5568 bytes: control archive=764 bytes.
      24 bytes,     1 lines      conffiles
     591 bytes,    13 lines      control
     289 bytes,     4 lines      md5sums
 Package: nvidia-docker2
 Version: 2.11.0~rc.4-1
 Architecture: all
 Maintainer: NVIDIA CORPORATION <cudatools@nvidia.com>
 Installed-Size: 27
 Depends: nvidia-container-toolkit (>= 1.10.0~rc.4-1), docker-ce (>= 18.06.0~ce~3-0~ubuntu) | docker-ee (>= 18.06.0~ce~3-0~ubuntu) | docker.io (>= 18.06.0) | moby-engine
 Breaks: nvidia-docker (<< 2.0.0)
 Replaces: nvidia-docker (<< 2.0.0)
 Section: utils
 Priority: optional
 Homepage: https://github.com/NVIDIA/nvidia-docker/wiki
 Description: nvidia-docker CLI wrapper
  Replaces nvidia-docker with a new implementation based on the NVIDIA Container Toolkit

Installing the new package:

$ sudo dpkg -i nvidia-docker2_2.11.0~rc.4-1_all.deb
Selecting previously unselected package nvidia-docker2.
(Reading database ... 173185 files and directories currently installed.)
Preparing to unpack nvidia-docker2_2.11.0~rc.4-1_all.deb ...
Unpacking nvidia-docker2 (2.11.0~rc.4-1) ...
Setting up nvidia-docker2 (2.11.0~rc.4-1) ...

And basic container functionality works as expected.

Signed-off-by: Evan Lezar elezar@nvidia.com