maas-test errors when the interface given on the command line has no IP address

[Raphaël Badin]

The DHCP detection code doesn't cope with a non-configured interface:

$ sudo ./bin/maas-test --bmc-mac aa:bb:cc:dd:ee:ff --bmc-username user --bmc-password pw eth0
2013-12-11 16:24:46,099 INFO Checking for KVM extensions.
2013-12-11 16:24:46,110 INFO Checking for virtualised hardware...
2013-12-11 16:24:46,163 INFO Scanning for unexpected DHCP servers on testing network...
Traceback (most recent call last):
  File "./bin/maas-test", line 9, in <module>
    load_entry_point('maas-test==0.1', 'console_scripts', 'maas-test')()
  File "/home/rvb/canonical/maas-test/maastest/main.py", line 62, in main
    dhcp_servers = probe_dhcp(args.interface)
  File "/home/rvb/canonical/maas-test/maastest/detect_dhcp.py", line 199, in probe_dhcp
    transaction_id = request_dhcp(interface)
  File "/home/rvb/canonical/maas-test/maastest/detect_dhcp.py", line 155, in request_dhcp
    bind_address = get_interface_IP(sock, interface)
  File "/home/rvb/canonical/maas-test/maastest/detect_dhcp.py", line 133, in get_interface_IP
    info = fcntl.ioctl(sock, SIOCGIFADDR, ifreq)
IOError: [Errno 99] Cannot assign requested address