bots: Add lorax-composer to rhel-7-6 image
bots: Add lorax-composer to rhel-7-6 image

Necessary for testing composer. It cannot install packages any more, as
this now requires a subscription.

Closes #10485

mvollmer/cockpit,moraleslazaro/cockpit,deryni/cockpit,deryni/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,deryni/cockpit,martinpitt/cockpit,cockpituous/cockpit,martinpitt/cockpit,cockpit-project/cockpit,cockpituous/cockpit,cockpituous/cockpit,cockpituous/cockpit,martinpitt/cockpit,deryni/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,andreasn/cockpit,mvollmer/cockpit,cockpit-project/cockpit,moraleslazaro/cockpit,andreasn/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,cockpituous/cockpit,andreasn/cockpit,deryni/cockpit,andreasn/cockpit,mvollmer/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,garrett/cockpit,garrett/cockpit,mvollmer/cockpit,garrett/cockpit,garrett/cockpit,deryni/cockpit,andreasn/cockpit,moraleslazaro/cockpit,deryni/cockpit,cockpit-project/cockpit,cockpituous/cockpit,andreasn/cockpit,cockpit-project/cockpit,garrett/cockpit,andreasn/cockpit