Ironic: set my_ip equal to local-ipv4 (if present)

Ironic (like Nova) uses my_ip as a default value for other settings.

One of those settings is the tftp_server address. By setting
the default TFTP address in this manner we avoid the need
to configure an explicit tftp_server unless a non-default
value is needed.

For me this simple fix resolved TFTP failures I recieved when
trying to use Ironic to provision real baremetal.

Change-Id: I744c3a91e5967bab7da9c73cdc8821851e8f7d4b
Partial-bug: #1318039
Merge "Ironic: set my_ip equal to local-ipv4 (if present)"