Duplicated ipmi address is not checked when creating or updating nodes

Ironic does not check duplicated ipmi address when creating or updating nodes, it leads to power sync problems.

As a demonstration, creates node A and B with identical ipmi address, and sets power state of node A to ON. Node A assumes target power state to ON, while node B assumes to OFF, the power of the real node will be switched back and forth during power state synchronization.

This case should be prevented by checking existing ipmi_address (and ipmi_port) when creating or updating a node to ironic, error should be returned when duplicated ipmi information is found.