Add trusty profile to cobbler.yaml

Add trusty profiles to cobbler.yaml. Default newly created nodes to
trusty profile. Add an example precise node showing how to select the
precise profile instead.

Change-Id: I5eb792eea9b359ae64bb48e24b80afc88517cebf
Partial-Bug: 1290508
Merge pull request #70 from CiscoSystems/bugs/1290508

Add trusty profile to cobbler.yaml