Make network configuration idempotent

[OpenStack Infra]

https://review.openstack.org/326367
Dear bug triager. This bug was created since a commit was marked with DOCIMPACT.

commit 8d06d9b28fc868ae982cb37a4708892a28d9d47a
Author: Aleksandr Didenko <email address hidden>
Date: Mon May 30 16:34:35 2016 +0200

    Make network configuration idempotent

    Remove configure_default_route task to make network configuration
    idempotent for majority of roles. 'Netconfig' task on all
    non-controller (except mongo) nodes will be executed after 'virtual_ips'
    task on controllers. So there's no need to reconfigure default route
    afterwards.

    Only mongo roles still have non-idempotent network configuration during
    the first deployment run, because mongo nodes are deployed before
    controllers in role-based deployment and no VIPs are configured yet.

    Also, instead of having one default gateway in Hiera and then replacing
    it with another one on the fly, let's create a new task that will simply
    put new gateway to Hiera and thus we'll have consistant configuration
    data for future runs of 'netconfig' task even on mongo roles.

    DocImpact

    Change-Id: I7269a6f632f9ab9c88d73be1ef6c04094c49889b
    Closes-bug: #1541309