Need to support static configuration of the mgmt interface

[jgruber]

When deploying VE with IPv6 networks, there is a desire to manually configure the mgmt interface without requiring SLAAC or DHCPv6 support. Currently the startup script only supports the configuring of TMM interfaces with static values.

Documentation on provisioning the management interface:

https://support.f5.com/kb/en-us/solutions/public/15000/000/sol15040.html

Since the mgmt interface provisioning is different then TMM interfaces, suggested userdata for mgmt interface should match how we provision the mgmt interface:

"network": {
    "interfaces": {
        "mgmt" : {
            "dhcp": "[true|false]",
            "address": "[ipv4 or ipv6 address]",
            "netmask": "[ipv4 netmask, ipv4 cidr bits count, ipv6 netmask, or ipv6 cidr bit count]",
            "ipv4_default_gateway": "[ipv4 address]",
            "ipv6_default_gateway": "[ipv6 address]"
        }
    }
}