Description of problem:
When virt-who work at xen mode, configure hypervisor_id=hostname/hwuuid can't work, virt-who can't send hostname and hwuuid to satellite.

Version-Release number of selected component (if applicable):
virt-who-0.17-8.el7.noarch
subscription-manager-1.17.10-1.el7.x86_64
python-rhsm-1.17.6-1.el7.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Register system to satellite5.7.
2. Configure virt-who run at xen mode and report host's name or hwuuid.
[root@hp-z220-03 virt-who.d]# cat /etc/virt-who.d/xen 
[test-xen]
type=xen
server=10.73.131.178
username=root
encrypted_password=cf0fc8adf1684c50644300e7cbd6a113
#password=Welcome1
owner=ACME_Corporation
env=Library
sat_server=10.73.3.209
sat_username=admin
sat_password=redhat
hypervisor_id=hwuuid   or hypervisor_id=hostname
3. Restart virt-who and check virt-who's log
[root@hp-z220-03 virt-who.d]#systemctl restart virt-who
[root@hp-z220-03 virt-who.d]#tail -f /var/log/rhsm/rhsm.log
2016-08-16 02:20:42,311 [virtwho.main INFO] MainProcess(17941):MainThread @satellite.py:hypervisorCheckIn:208 - Sending update in hosts-to-guests mapping: 1 hypervisors and 0 guests found
2016-08-16 02:20:42,311 [virtwho.main DEBUG] MainProcess(17941):MainThread @satellite.py:hypervisorCheckIn:210 - Host-to-guest mapping: {
    "hypervisors": [
        {
            "hypervisorId": {
                "hypervisorId": "4cc99f10-42ea-40f3-bbc5-ca1a7f8aa903"
            }, 
            "name": "xenserver-dagelflw", 
            "guestIds": [], 
            "facts": {
                "hypervisor.type": "XenServer", 
                "cpu.cpu_socket(s)": "2", 
                "hypervisor.version": "7.0.0"
            }
        }
    ]
}
2016-08-16 02:20:42,311 [virtwho.main DEBUG] MainProcess(17941):MainThread @satellite.py:hypervisorCheckIn:215 - Loading systemid for 4cc99f10-42ea-40f3-bbc5-ca1a7f8aa903

Actual results:
Virt-who still send hostuuid(""hypervisorId": "4cc99f10-42ea-40f3-bbc5-ca1a7f8aa903"") to server.

Expected results:
Virt-who should send hostname/hwuuid to server according to config.

Additional info: