Description of problem:
When virt-who run with CLI at remote libvirt mode without env/owner, it will show "Traceback (most recent call last):" in terminal.

Version-Release number of selected component (if applicable):
virt-who-0.17-10.el7.noarch
subscription-manager-1.17.11-1.el7.x86_64
python-rhsm-1.17.7-1.el7.x86_64

How reproducible:
Always

Steps to Reproduce:
1. Register system to satellite6.2
2. Run virt-who with CLI without env/owner in remote libvirt mode.
[root@hp-z220-08 virt-who.d]# virt-who --libvirt --libvirt-owner=111 --libvirt-env= --libvirt-server=hp-z220-06.qe.lab.eng.nay.redhat.com --libvirt-username=root --libvirt-password= -d --satellite6
Option `env` needs to be set in config `env/cmdline`
Traceback (most recent call last):
  File "/usr/lib/python2.7/site-packages/virtwho/__main__.py", line 8, in main
    res = virtwho.main.main()
  File "/usr/lib/python2.7/site-packages/virtwho/main.py", line 132, in main
    config.checkOptions(logger)
  File "/usr/lib/python2.7/site-packages/virtwho/config.py", line 291, in checkOptions
    raise InvalidOption("Option `env` needs to be set in config `%s`" % (self.name))
InvalidOption: Option `env` needs to be set in config `env/cmdline`
No handlers could be found for logger "virtwho.main"
2016-09-02 04:34:04,081 [virtwho.init DEBUG] MainProcess(1345):MainThread @executor.py:terminate:303 - virt-who is shutting down

Actual results:
It will show some traceback info in terminal.

Expected results:
It shouldn't show traceback info in terminal, it should only show remind info as the following:
Option --libvirt-env (or VIRTWHO_LIBVIRT_ENV environment variable) needs to be set

Additional info:
It hasn't this problem when virt-who run at hyperv mode in the same condition:
[root@hp-z220-08 virt-who.d]# virt-who --hyperv --hyperv-env=Library --hyperv-server=10.73.131.228 --hyperv-username=administrator --hyperv-password=Welcome1 -o -d
Option --hyperv-owner (or VIRTWHO_HYPERV_OWNER environment variable) needs to be set