Change all occurences of no_delete to do_delete

Change all occurences of no_delete to do_delete

Previously, ports, networks and subnets had a do_delete=True
parameter. By default, these resources were deleted at the
end of the context manager scope. All other resources used
a different semantic: no_delete=False.

This caused confusing situations such as:
with self.subnet(network, do_delete=False) as subnet:
    with self.security_group(no_delete=True) as sg:
        pass

Now all resources use the same do_delete semantic.

Closes-Bug: #1336196
Change-Id: I4627481813f714819efe85831e2a55975ea71ed4