Disable registration on CentOS images
Disable registration on CentOS images

When building CentOS images, disable the image registration (usually
with subscription-manager, which is RHEL-only).

Due to a bug in diskimage-builder [1], we need to temporarly export
REG_HALT_UNREGISTER=1 to prevent unregistration too.

[1] https://review.openstack.org/#/c/162239/

Change-Id: I47d2c1f6576700d9eb56ecceac1e19c2b40e8297

openstack/sahara-image-elements,uladz/sahara-image-elements,uladz/sahara-image-elements,bigfootproject/sahara-image-elements,openstack/sahara-image-elements,crobby/sahara-image-elements,bigfootproject/sahara-image-elements,crobby/sahara-image-elements