Better feedback from dhcp assoc

[paalbra]

Feedback from dhcp assoc could be better if you try to associate the a MAC an IP that already has the MAC associated.

TEST> host info xxx.example.com                                                                                                                    
Name:         xxx.example.com
Contact:      
A_Records     IP              MAC
              10.0.0.100      00:11:22:33:aa:bb
TTL:          (Default)
TEST> dhcp assoc xxx.example.com 00:11:22:33:aa:bb                                                                                                 
WARNING: : mac 00:11:22:33:aa:bb already in use by: 10.0.0.100. Use force to add 10.0.0.100 -> 00:11:22:33:aa:bb as well.
TEST> dhcp assoc xxx.example.com 00:11:22:33:aa:bb -force                                                                                          
OK: : new and old mac are identical. Ignoring.
OK: : associated mac address None with ip 10.0.0.100