esx: Allow to configure static IPs

[pothos]

• esx: Allow to configure static IPs
  The default ESXi setup does not have a DHCP server but expects
  static IPs to be used (e.g., see https://www.packet.com/resources/guides/esxi/).
  Allocate static IPs for each machine from a number of addresses
  starting with a specific address given inside the subnet (in Packet this
  is the next IP address after the host's IP, see link above).
  A networkd configuration file is used with Ignition but cloud-config writes its
  own networkd configuration file based on the guestinfo.interface* variables.
  The coreos-metadata service uses the COREOS_CUSTOM_* variables that are known
  to the Container Linux Config Transpiler, too, and got some robustness fixes.

How to use

./kola run -d --platform esx --esx-config-file esx.json --esx-ova-path flatcar_production_vmware_ova.ova  --esx-first-static-ip A.B.C.D --esx-first-static-ip-private E.F.G.H --esx-static-ips 4 --esx-gateway I.J.K.L --esx-gateway-private M.N.O.P --esx-subnet-size 29

Because we only have 4 static IPs, do not set --parallel X because kola will wait anyway until a machine terminates again and frees an IP.

Testing done

Use an ESX server on Packet and use the gateways as visible in the network setting of the Packet web UI, and use the next IP after the server IP as available first static IPs (see link above). When the ESX server is provisioned, a /28 subnet can be specified instead of the defautl /29 but I didn' test this.
I fixed most test failures and skipped tests that rely on network connectivity in the initramfs.

[pothos]

This is ready for review now. I'll switch back to ignition.config variables once flatcar/coreos-cloudinit#4 is referenced in coreos-overlay.