Changing compression from .tar.gz to .tar.xz
Changing compression from .tar.gz to .tar.xz

As per psedlak request, the compression level for .xz is bigger than
.gz making the artifacts smaller.

okolisny/InfraRed,okolisny/InfraRed,okolisny/InfraRed,redhat-openstack/infrared,redhat-openstack/infrared,redhat-openstack/infrared