Added check to see if the variable file is empty
Added check to see if the variable file is empty

The `pw-token-gen.py` script will fail if used against an empty file.
This change adds a None type check and returns an exit error and
messaage if the loaded value is None.

Closes-Bug: 1446338
Change-Id: I83cb9d1ef312f870f555c6de5f42815ba40e895e

wenhuizhang/os-ansible-deployment,cfarquhar/openstack-ansible,shane-c/openstack-ansible,yanyao/openstack-deployment-liberty,yanyao/newton,wenhuizhang/os-ansible-deployment,yanyao/newton,jpmontez/os-ansible-deployment,pombredanne/os-ansible-deployment,shane-c/openstack-ansible,achekunov/openstack-ansible,os-cloud/os-ansible-deployment,pombredanne/os-ansible-deployment,mrda/openstack-ansible,git-harry/os-ansible-deployment,sacharya/os-ansible-deployment,dhanunjaya/os-ansible-deployment,major/openstack-ansible,git-harry/os-ansible-deployment,mrda/openstack-ansible,robb-romans/openstack-ansible,jpmontez/openstack-ansible,robb-romans/openstack-ansible,jpmontez/os-ansible-deployment,BjoernT/openstack-ansible,BjoernT/os-ansible-deployment,manuelfelipe/openstack-ansible,stackforge/os-ansible-deployment,open-switch/infra_openstack-ansible,sigmavirus24/os-ansible-deployment,stackforge/os-ansible-deployment,bunchc/openstack-ansible,yanyao/openstack-deployment-liberty,jpmontez/openstack-ansible,sti-jans/openstack-ansible,antonym/openstack-ansible,achekunov/openstack-ansible,major/os-ansible-deployment,d34dh0r53/os-ansible-deployment,shane-c/openstack-ansible,miguelgrinberg/os-ansible-deployment,open-switch/infra_openstack-ansible,git-harry/os-ansible-deployment,sigmavirus24/openstack-ansible,sigmavirus24/os-ansible-deployment,cloudnull/os-ansible-deployment,BjoernT/os-ansible-deployment,yanyao/openstack-deployment-liberty,metral/os-ansible-deployment,weezer/openstack-ansible,sti-jans/openstack-ansible,manuelfelipe/openstack-ansible,achekunov/openstack-ansible,BjoernT/openstack-ansible,manuelfelipe/openstack-ansible,AlphaStaxLLC/os-ansible-deployment,open-switch/infra_openstack-ansible,AlphaStaxLLC/os-ansible-deployment,major/openstack-ansible,Logan2211/openstack-ansible,jpmontez/os-ansible-deployment,antonym/openstack-ansible,pombredanne/os-ansible-deployment,yanyao/openstack-ansible,antonym/openstack-ansible,cfarquhar/openstack-ansible,openstack/openstack-ansible,AlphaStaxLLC/os-ansible-deployment,openstack/openstack-ansible,mancdaz/openstack-ansible,miguelgrinberg/os-ansible-deployment,metral/os-ansible-deployment,os-cloud/os-ansible-deployment,weezer/openstack-ansible,Logan2211/openstack-ansible,BjoernT/os-ansible-deployment,yanyao/openstack-ansible,mrda/openstack-ansible,major/os-ansible-deployment,mancdaz/openstack-ansible,d34dh0r53/os-ansible-deployment,sti-jans/openstack-ansible,bunchc/openstack-ansible,dhanunjaya/os-ansible-deployment,jpmontez/openstack-ansible,sacharya/os-ansible-deployment,sigmavirus24/openstack-ansible,cloudnull/os-ansible-deployment