containers: adjust environment for build changes
containers: adjust environment for build changes

 - stop using NO_DIST_CACHE=1 (we never build the cache anymore)

 - XZ_OPT is the new XZ_COMPRESS_FLAGS

cockpit-project/cockpit,garrett/cockpit,martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,garrett/cockpit,cockpit-project/cockpit,garrett/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,garrett/cockpit,garrett/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,mvollmer/cockpit