CI: streamline packet jobs definition

- Take advantage of `parallel:matrix` to make the jobs definition shorter
  and more readable.
- Remove helper scripts which are no longer needed
- Remove redundant indirection in the gitlab-ci pipelines definitions
  (only one user)

tests/scripts/testcases_run.sh

@@ -1,19 +1,9 @@
 #!/bin/bash
 set -euxo pipefail
 
-echo "CI_JOB_NAME is $CI_JOB_NAME"
+echo "TESTCASE is $TESTCASE"
 
-if [[ "$CI_JOB_NAME" =~ "upgrade" ]]; then
-  if [ "${UPGRADE_TEST}" == "false" ]; then
-    echo "Job name contains 'upgrade', but UPGRADE_TEST='false'"
-    exit 1
-  fi
-else
-  if [ "${UPGRADE_TEST}" != "false" ]; then
-    echo "UPGRADE_TEST!='false', but job names does not contain 'upgrade'"
-    exit 1
-  fi
-fi
+source tests/files/$TESTCASE || true
 
 # Check out latest tag if testing upgrade
 if [ "${UPGRADE_TEST}" != "false" ]; then
@@ -31,7 +21,7 @@ make -C tests create-${CI_PLATFORM} -s
 # Test collection build and install by installing our collection, emptying our repository, adding
 # cluster.yml, reset.yml, and remote-node.yml files that simply point to our collection's playbooks, and then
 # running the same tests as before
-if [[ "${CI_JOB_NAME}" =~ "collection" ]]; then
+if [[ "${TESTCASE}" =~ "collection" ]]; then
   # Build and install collection
   ansible-galaxy collection build
   ansible-galaxy collection install kubernetes_sigs-kubespray-$(grep "^version:" galaxy.yml | awk '{print $2}').tar.gz
@@ -69,7 +59,7 @@ shift
 # We can set --limit here and still pass it as supplemental args because `--limit`  is a 'last one wins' option
 ansible-playbook \
     -e @tests/common_vars.yml \
-    -e @tests/files/${CI_JOB_NAME}.yml \
+    -e @tests/files/${TESTCASE}.yml \
     -e local_release_dir=${PWD}/downloads \
     "$@" \
     ${playbook}
@@ -111,10 +101,10 @@ run_playbook tests/testcases/015_check-nodes-ready.yml
 
 ## Test that all nodes are Ready
 
-if [[ ! ( "$CI_JOB_NAME" =~ "macvlan" ) ]]; then
+if [[ ! ( "$TESTCASE" =~ "macvlan" ) ]]; then
     run_playbook tests/testcases/020_check-pods-running.yml
     run_playbook tests/testcases/030_check-network.yml
-    if [[ ! ( "$CI_JOB_NAME" =~ "hardening" ) ]]; then
+    if [[ ! ( "$TESTCASE" =~ "hardening" ) ]]; then
       # TODO: We need to remove this condition by finding alternative container
       # image instead of netchecker which doesn't work at hardening environments.
       run_playbook tests/testcases/040_check-network-adv.yml