baremetal: Change node api related to prov_mac_address

Now prov_mac_address is going to be dropped from bm_nodes table. This patch
adjust api to the change.

A user is expected to create a node without specifying prov_mac_address, then add
an interface having the address to the node. However, for compatibility, a user
still can specify prov_mac_address when create a node. In this case, an interface
having prov_mac_address is automatically added to the node.

In response body of create, index and show, "prov_mac_address" field no longer
exists since they are showed as a member of "interfaces" fileld.

DocImpact

Change-Id: I6653829364b0a641442d45e766493180d6f2a880
Merge "baremetal: Change node api related to prov_mac_address"