Drop `bm_pxe_ips` table from baremetal database.

- added migration and tests
- removed model `BareMetalPxeIp`
- from nova/virt/baremetal/db/sqlalchemy/api.py removed functions
 `bm_pxe_ip_get_all`, `bm_pxe_ip_create`, `bm_pxe_ip_create_direct`,
 `bm_pxe_ip_destroy`, `bm_pxe_ip_destroy_by_address`, 'bm_pxe_ip_get`,
 `bm_pxe_ip_get_by_bm_node_id`, `bm_pxe_ip_associate`, 'bm_pxe_ip_disassociate`
- from nova/virt/baremetal/db/api.py removed functions
 `bm_node_associate_and_update`, `bm_pxe_ip_create`, `bm_pxe_ip_create_direct`,
 `bm_pxe_ip_destroy`, `bm_pxe_ip_destroy_by_address`, `bm_pxe_ip_get_all`,
 `bm_pxe_ip_get`, `bm_pxe_ip_get_by_bm_node_id, `bm_pxe_ip_associate`,
 `bm_pxe_ip_disassociate`
- from nova/tests/virt/baremetal/db/utils.py removed function `new_bm_pxe_ip`
- removed nova/tests/virt/baremetal/db/test_bm_pxe_ip.py
- modified `baremetal/volume_driver.py` - now we get `address` using
  nova db api

Fixes bug 1156745

Change-Id: I61f78d692da276694d79a7c1a8d45a466d124c70
Merge "Drop `bm_pxe_ips` table from baremetal database."