Support mapping compute & login instances to Ironic nodes

[sjpb]

Adds support for mapping baremetal compute and/or login nodes to ironic hosts with the same names, e.g:

# environments/$env/terraform/terraform.tfvars:
...
cluster_name = "mycloud"
login_nodes = {
    login-0 = {
        flavor: "baremetal.highmem"
        match_ironic_node: true
    }
}
compute = {
    hpc = {
        flavor = "baremetal.xlarge"
        match_ironic_node: true
        availability_zone = "az2"
        nodes = ["hpc-0", "hpc-1", "hpc-2"]
    }
}
...

will result in:

• An instance named mycloud-login-0 on ironic node login-0 in the default "nova" availability zone
• Compute instances mycloud-hpc-N on ironic nodes hpc-N in the "az2" availability zone

[sjpb]

Tested it works on a cloud without baremetal service, without admin creds.

[jovial]

Looks good to me