Only display networks for which a node has an IP address

On the show node page, we were displaying all networks known to a node,
including the ones that don't have any IP address associated to any
interface. This is kind of useless (if there's no BMC, for instance).

Instead, we only display networks for which there's an IP address.
Show DHCP IP address when node is being discovered

When ta node is being discovered, it's using a temporary DHCP address,
and not the IP addresses defined with the network cookbook.

It's useful for people to know the temporary IP address so they can log
in the sledgehammer image if needed.
Merge pull request #744 from vuntz/only-display-relevant-ips

Only display relevant IP addresses on the node page
+1 tested
wait with reboot for the finish of configuration update by local chef-client
Merge pull request #772 from jsuchome/release/roxy/master

+1 wait with reboot for the finish of configuration update by local chef-client
use attr_accessor instead of defining the methods manually
Merge pull request #781 from mapleoin/attr-accessor

use attr_accessor instead of defining the methods manually
get rid of redefinition of 'initialize'
Merge pull request #780 from mapleoin/redef

get rid of redefinition of 'initialize'