Display container ip not gateway IP

As described in the attribute schema of network_ip we want to show the
container ip and not the gateway ip.

Change-Id: I86a3c3476d04d437d7b6bb270d3178d0bc7e8136
Partial-Bug: #1296745
Add docker network_gateway attribute

We previously had it in network_ip attribute when that value should have
been the container ip. Add a new value called network_gateway giving
this information to the user.

Change-Id: I8ebfc576f4bbc470aa2d405e8b063932017904cc
Closes-Bug: 1296745
Merge "Display container ip not gateway IP"
Merge "Add docker network_gateway attribute"