test: Add rhel-7.4 testing
test: Add rhel-7.4 testing

Let our testing infrastructure become aware of rhel-7.4 testing.

Closes #6559

Scribery/cockpit,larsu/cockpit,martinpitt/cockpit,petervo/cockpit,larskarlitski/cockpit,moraleslazaro/cockpit,deryni/cockpit,stefwalter/cockpit,mareklibra/cockpit,cockpituous/cockpit,stefwalter/cockpit,Scribery/cockpit,moraleslazaro/cockpit,stefwalter/cockpit,larskarlitski/cockpit,Scribery/cockpit,Scribery/cockpit,petervo/cockpit,andreasn/cockpit,cockpituous/cockpit,SotolitoLabs/cockpit,mvollmer/cockpit,petervo/cockpit,michalskrivanek/cockpit,moraleslazaro/cockpit,deryni/cockpit,moraleslazaro/cockpit,Scribery/cockpit,SotolitoLabs/cockpit,petervo/cockpit,garrett/cockpit,mareklibra/cockpit,xhad/cockpit,andreasn/cockpit,xhad/cockpit,Scribery/cockpit,stefwalter/cockpit,deryni/cockpit,xhad/cockpit,petervo/cockpit,Scribery/cockpit,garrett/cockpit,moraleslazaro/cockpit,larskarlitski/cockpit,garrett/cockpit,michalskrivanek/cockpit,larskarlitski/cockpit,mareklibra/cockpit,mvollmer/cockpit,garrett/cockpit,larskarlitski/cockpit,dperpeet/cockpit,petervo/cockpit,SotolitoLabs/cockpit,mareklibra/cockpit,larsu/cockpit,mareklibra/cockpit,mareklibra/cockpit,xhad/cockpit,deryni/cockpit,larskarlitski/cockpit,martinpitt/cockpit,andreasn/cockpit,deryni/cockpit,cockpituous/cockpit,SotolitoLabs/cockpit,stefwalter/cockpit,martinpitt/cockpit,harishanand95/cockpit,michalskrivanek/cockpit,cockpituous/cockpit,mareklibra/cockpit,dperpeet/cockpit,cockpituous/cockpit,harishanand95/cockpit,larsu/cockpit,SotolitoLabs/cockpit,cockpit-project/cockpit,dperpeet/cockpit,SotolitoLabs/cockpit,dperpeet/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,cockpituous/cockpit,michalskrivanek/cockpit,xhad/cockpit,larsu/cockpit,michalskrivanek/cockpit,michalskrivanek/cockpit,larskarlitski/cockpit,harishanand95/cockpit,andreasn/cockpit,andreasn/cockpit,stefwalter/cockpit,cockpit-project/cockpit,andreasn/cockpit,SotolitoLabs/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,xhad/cockpit,deryni/cockpit,deryni/cockpit,larsu/cockpit,harishanand95/cockpit,larsu/cockpit,michalskrivanek/cockpit,moraleslazaro/cockpit,stefwalter/cockpit,xhad/cockpit,dperpeet/cockpit,harishanand95/cockpit,garrett/cockpit,petervo/cockpit,mvollmer/cockpit,andreasn/cockpit,mvollmer/cockpit,harishanand95/cockpit,cockpit-project/cockpit,dperpeet/cockpit,dperpeet/cockpit,harishanand95/cockpit