Enable testing on centos7

Signed-off-by: Cristian Le <git@lecris.dev>

Author: LecrisUT

tests/prepare/artifact/install-cases.sh

@@ -47,8 +47,6 @@ xfail_plans_nobest=(
         extra_env=""
         if is_centos_7 "$image"; then
              extra_env="-e DNF_CMD=yum"
-            # TODO: centos7 is hard
-            continue
         fi
 
         phase_prefix="$(test_phase_prefix $image)"