Datasource for VMware

This patch finally introduces the Cloud-Init Datasource for VMware
GuestInfo as a part of cloud-init proper. This datasource has existed
since 2018, and rapidly became the de facto datasource for developers
working with Packer, Terraform, for projects like kube-image-builder,
and the de jure datasource for Photon OS.

The major change to the datasource from its previous incarnation is
the name. Now named DatasourceVMware, this new version of the
datasource will allow multiple transport types in addition to
GuestInfo keys.

This datasource includes several unique features developed to address
real-world situations:

  * Support for reading any key (metadata, userdata, vendordata) both
    from the guestinfo table when running on a VM in vSphere as well as
    from an environment variable when running inside of a container,
    useful for rapid dev/test.

  * Allows booting with DHCP while still providing full participation
    in Cloud-Init instance data and Jinja queries. The netifaces library
    provides the ability to inspect the network after it is online,
    and the runtime network configuration is then merged into the
    existing metadata and persisted to disk.

  * Advertises the local_ipv4 and local_ipv6 addresses via guestinfo
    as well. This is useful as Guest Tools is not always able to
    identify what would be considered the local address.

The primary author and current steward of this datasource spoke at
Cloud-Init Con 2020 where there was interest in contributing this datasource
to the Cloud-Init codebase.

The datasource currently lives in its own GitHub repository at
https://github.com/vmware/cloud-init-vmware-guestinfo. Once the datasource
is merged into Cloud-Init, the old repository will be deprecated.

cloudinit/settings.py

@@ -43,6 +43,7 @@
         'Exoscale',
         'RbxCloud',
         'UpCloud',
+        'VMware',
         # At the end to act as a 'catch' when none of the above work...
         'None',
     ],