Add support for node groups in NetConfigDataLookup

Add support for node groups in NetConfigDataLookup

By using DMI String as identifier, such as 'system-product-name'
or 'system-version' add support for node groups. This allow the
use of a single entry in 'NetConfigDataLookup' to match a group
of systems of the same model, vendor etc.

Try to match on ethernet mac address first, then if no match is
found 'dmiString' and 'id' is used, if the keys are set.

Example:

  NetConfigDataLookup:
    node1:
      nic1: "00:c8:7c:e6:f0:2e"
    node2:
      nic1: "00:18:7d:99:0c:b6"
    node3:
      dmiString: 'system-version'
      id: 'ThinkPad T460p'
      nic1: enp0s31f6
    # Dell PowerEdge R630 - nodegroup
    nodegroup1:
      dmiString: "system-product-name"
      id: "PowerEdge R630"
      nic1: em3
      nic2: em1
      nic3: em2
    # Cisco UCS B200-M4 - nodegroup
    nodegroup2:
      dmiString: "system-product-name"
      id: "UCSB-B200-M4"
      nic1: enp7s0
      nic2: enp6s0

Change-Id: Ie2547cd8805c57ed9afe7362eada802580ffc215