Introduce interface type "bmc" for managing BMC via DHCP.
Make pre_install_network_config to ignore BMC interface.
Make network_config to ignore BMC interface.
Make network_config_esx to ignore BMC interface.
Make network_config_esxi to ignore BMC interface.
Make post_install_network_config to ignore BMC interface.
Make post_install_network_config_deb to ignore BMC interface.
Merge pull request #1197 from r0ckpine/feature/bmc-interface

Introduce interface type "bmc" for managing BMC via DHCP.