[xenserver] added missing HostCpu model
[xenserver] added missing host_cpus attribute to Host model
[xenserver|tests] added HostCpu model tests
[xenserver|tests] typo fix
[xenserver|tests] test Host.host_cpus method
[xenserver] add missing Host attributes (edition, software_version)
[xenserver] replace #connection with #service in models

connection is now deprecated as per #1415, #1392
Merge pull request #1453 from rubiojr/add-host-cpu-model

[xenserver] Added HostCpu model