Create system tests for Linux bonds and bridges feature

We need additional system tests which deploy Fuel with Linux bonds/bridges (feature blueprint: https://blueprints.launchpad.net/fuel/+spec/refactor-l23-linux-bridges) and check that:

- network devices are configured correctly (e.g. devices combined to bond or correct MTU value is set for port);
- cluster passes network verification;
- cluster passes health checks.

Existing tests for 'interfaces bonding' feature should be modified, so we can use granular deployment feature:

- configure cluster and network at first step;
- deploy network (and required for it granules) at second step;
- check that bonds are configured and have correct settings (e.g. balancing mode) at third step;
- deploy all the rest granules and run OSTF on last step.