Description of problem:
When It hasn't configured env option against stage candlepin, virt-who can't be started.

Version-Release number of selected component (if applicable):
virt-who-0.17-7.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 stage candlepin.

2. Start virt-who in CLI without env option.
# virt-who --xen --xen-owner=7970632 --xen-server=10.73.131.183 --xen-username=root --xen-password=Welcome1 -o -d
Option --xen-env (or VIRTWHO_XEN_ENV environment variable) needs to be set

3. Configure virt-who in /etc/virt-who.d/xxx or /etc/sysconfig/virt-who without env
# cat /etc/virt-who.d/virt
[xen]
type=xen
server=10.73.131.183
username=root
password=Welcome1
owner=7970632
env= 
# systemctl restart virt-who.service
Job for virt-who.service failed because the control process exited with error code. See "systemctl status virt-who.service" and "journalctl -xe" for details.

# systemctl status virt-who.service
● virt-who.service - Daemon for reporting virtual guest IDs to subscription-manager
   Loaded: loaded (/usr/lib/systemd/system/virt-who.service; disabled; vendor preset: disabled)
   Active: failed (Result: exit-code) since Wed 2016-08-17 14:37:04 EDT; 806ms ago
  Process: 18350 ExecStart=/usr/bin/virt-who (code=exited, status=1/FAILURE)
 Main PID: 18350 (code=exited, status=1/FAILURE)
   Status: "virt-who can't be started: Option --xen-env (or VIRTWHO_XEN_ENV environment variable) needs to be set"

Actual results:
Failed to start virt-who as it hasn't configure env.

Expected results:
Virt-who should be started normally although it hasn't configure env option when it work with stage candlepin Since "The thing is that *env switches are not handled by Candlepin itself. The env swiches are used to do authentication against other Sat 6 products (e.g. Katello)"(Refer to bug 1235980 comment 10).

Additional info: