902804: Properly init consumer guestIds to empty

When the HypervisorResource creates a host consumer,
but doesn't associate a guestId, the consumer's guestId
list would remain null. This was causing issues for any
caller that relied upon this guestid list (virt-who).

By properly initializing the list to an empty one, we
are guaranteed [] in the resulting JSON.
902804: Do not include new consumer in result.updated

This commit reworks how host consumers are added to the
result of the HypervisorResource.hypervisorCheckin.

result.created - Any new host consumers.
result.updated - Any host who's guest ids were updated.
result.unchanged - Any host that was reported, but has
                   the same guest ids.
result.failure - Any failure that occured (per host)
Merge pull request #171 from candlepin/mstead/hypervisor-resource-changes

Changes to HypervisorResource that addresses BZ 902804