Add bridge support for the HTTP API and CLI

[teclator]

Problem

Although there is a bridge model in the backend, there is no way to configure it through the CLI or through the HTTP api.

• https://trello.com/c/LoDehu4m/4559-1-agama-add-support-for-configuring-a-bridge

Solution

Added bridge support similar to what was added for bonding in (#885) and also fix it because looks like we broke the bonding handling when moved to the HTTP Api (#1064).

An example of the json bridge configuration looks like:

{
  "network": {
    "connections": [
      {
        "id": "Bridge0",
        "method4": "manual",
        "interface": "br0",
        "addresses": ["192.168.1.100/24"],
        "gateway4": "192.168.1.1",
        "nameservers": ["192.168.1.1"],
        "bridge": {
          "ports": ["eth0", "eth1"],
          "stp": false
        }
      }
    ]
  }
}

Testing

• Added a new unit test
• Tested manually

[coveralls]

coverage: 63.008% (+0.2%) from 62.83%
when pulling f1ae5d6 on bridge_support
into c008d8f on master.

[imobachgs]

The approach looks good (similar to the bonding support), but there is too much cloning.