cloud-init does not recognize initramfs provided network config in all cases

Cloud-init relies on the 'ip=' or 'ip6=' parameter to be present in the
kernel command line in order to consider /run/net-*.conf files. Those files
are written by the initramfs indicating that network is was configured.

When 'ip=' or 'ip6=' is found on the command line, cloud-init will consider
that to be "kernel command line provided" network, and renders a network
configuration like:
  # control-manual ens3
  iface ens3 inet dhcp
      broadcast 10.0.3.255
      dns-nameservers 169.254.169.254
      gateway 10.0.3.1

The key there being that it is not marked 'auto'. If cloud-init does
not recognize this, it will render:
  auto ens3
  iface ens3 inet dhcp

There are some iscsi-root where initramfs configures networking
but the ip= parameter is not present. 2 such cases are:
 a.) static config in /etc/iscsi/iscsi.initramfs (copied into the initramfs)
 b.) iBft

If the devices are marked 'auto', then 'networking.service' takes
the device down during shutdown. That causes any filesystem activity
to hang and block shutdown/reboot.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: cloud-init 17.1-46-g7acc9e68-0ubuntu1~16.04.1 [modified: usr/lib/python3/dist-packages/cloudinit/net/cmdline.py usr/lib/python3/dist-packages/cloudinit/sources/helpers/openstack.py]
ProcVersionSignature: Ubuntu 4.4.0-108.131-generic 4.4.98
Uname: Linux 4.4.0-108-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.15
Architecture: amd64
CloudName: OpenStack
Date: Wed Feb 28 18:35:50 2018
PackageArchitecture: all
ProcEnviron:
 TERM=xterm-256color
 PATH=(custom, no user)
 LANG=en_US.UTF-8
 SHELL=/bin/bash
SourcePackage: cloud-init
UpgradeStatus: No upgrade log present (probably fresh install)