providers/vmware: support injecting custom network kargs

[lucab]

This implements fetching logic specific to the vmware provider
in order to support injecting custom network kargs, which are meant
to override the default ones.

In particular, this checks for an optional guestinfo property named
guestinfo.afterburn.initrd.network-kargs which can be used to provide
a string containing VM-specific overrides.

[jcpowermac]

@lucab I was following the closed PR.
I would assume that vmtoolsd would need to be running before trying to query for guestinfo?
Could we use this to set the hostname?

cc:
@mtnbikenc
@patrickdillon

[lucab]

I would assume that vmtoolsd would need to be running before trying to query for guestinfo?

No, this has no dependency on vmtoolsd. Like Ignition, it queries the hypervisor back-channel directly. At the time when this (and Ignition) runs in initramfs, it is quite too early for vmtoolsd.

Could we use this to set the hostname?

Possibly, if you already have it as part of your ip= and if that works generally.
However, I'd recommend against approaching it that way as it is fragile (as we keep finding out, see e.g. coreos/fedora-coreos-tracker#466)
Hostname should be coming from DHCP. If that is missing or needs to be overridden, static hostname configuration should be performed via Ignition configuration (like all other OS customizations).

[lucab]

Rebased against master, this is ready for review. CI is green and I manually tested on a vSphere setup with static networking.

/cc @jlebon