Add default_boot_option configuration
Add default_boot_option configuration

The default value of default_boot_option configuration will
change eventually from "netboot" to "local".
It is recommended to set an explicit value for it during the
transition period

Change-Id: Ic42b84e82d4ad27e371536ad9915b5a32118012d
Closes-Bug: #1696636

dardelean/kolla-ansible,dardelean/kolla-ansible,dardelean/kolla-ansible