e2e-k8s.sh: don't manipulate SKIP when LABEL_FILTER is used

It's unexpected when a job runs a different set of tests than specified by
LABEL_FILTER. Not only that, at least for periodic jobs it would be desirable
to have only one variant of the job which runs all tests (serial and parallel),
with parallel execution of the parallel tests. Maintaining two variants is more
work and makes the testgrid dashboards larger.

This change does not affect jobs that don't use LABEL_FILTER because the
traditional behavior is preserved for those.

It does affect the following jobs (based on "grep 'name: LABEL_FILTER'"):

  - pull-kind-conformance-parallel-dual-stack-ipv4-ipv6
  - pull-kind-e2e-kubernetes
  - pull-kind-e2e-kubernetes-canary
  - ci-kubernetes-kube-network-policies-conformance-parallel
  - ci-kubernetes-kube-network-policies-conformance-parallel-ipv6
  - pull-kube-network-policies-nftables
  - pull-kube-network-policies-nftables-ipv6
  - pull-kubernetes-e2e-kind-dependencies (also for 1.34)
  - pull-kubernetes-e2e-kind-golang-tip (also for 1.34)
  - ci-kubernetes-e2e-kind-dependencies (also for 1.34)
  - ci-kubernetes-e2e-kind-golang-tip (also for 1.34)
  - ci-kubernetes-kind-e2e-json-logging (also in release branches)
  - ci-kubernetes-network-kind-alpha-beta-features
  - ci-kubernetes-e2e-kind (also for 1.34)
  - ci-kubernetes-e2e-kind-ipv6
  - ci-kubernetes-e2e-kind-beta-features
  - ci-kubernetes-e2e-kind-alpha-beta-features
  - pull-kubernetes-e2e-kind
  - pull-kubernetes-e2e-kind-canary
  - pull-kubernetes-e2e-kind-ipv6
  - pull-kubernetes-e2e-kind-ipv6-canary
  - pull-kubernetes-e2e-kind-beta-features
  - pull-kubernetes-e2e-kind-beta-enabled
  - pull-kubernetes-e2e-kind-beta-enabled-conformance
  - pull-kubernetes-e2e-kind-alpha-beta-features
  - pull-kubernetes-e2e-kind-alpha-beta-enabled
  - pull-kubernetes-e2e-kind-alpha-beta-enabled-conformance
  - pull-kubernetes-e2e-kind-alpha-beta-features-race
  - pull-kubernetes-e2e-kind-evented-pleg
  - pull-kubernetes-e2e-storage-kind-alpha-beta-features-slow

kube-network-policies already ran serial conformance tests ('|| Conformance'),
but not normal serial tests.

Some other jobs using LABEL_FILTER already explicitly disabled serial tests and
thus get the same behavior as before.

The first two are inconsistent at the moment: pull-kind-e2e-kubernetes is
probably meant to run more than conformance tests and correctly does so by not
setting FOCUS. pull-kind-conformance-parallel-dual-stack-ipv4-ipv6 is meant
to be limited to conformance, but does not filter by that in LABEL_FILTER and
thus runs also non-conformance tests because the FOCUS default already got
disabled earlier when using LABEL_FILTER.

Other jobs may need an explicit "!Serial", depending on the intention of the job
owner, before the e2e-k8s.sh can be changed.

Author: pohly

hack/ci/e2e-k8s.sh

@@ -246,6 +246,15 @@ run_tests() {
   fi
 
   # ginkgo regexes and label filter
+  #
+  # Defaults for FOCUS and SKIP only get set when the job hasn't been converted
+  # to use LABEL_FILTER. This emulates the historic behavior while making
+  # updated jobs easier to read ("what you see is what you get").
+  #
+  # It also enables jobs where all tests (serial and parallel) run with
+  # parallel execution of the parallel tests, followed by sequential execution
+  # of the serial ones. This has been supported since Ginkgo v2 but not by
+  # this script because of the mandatory SKIP="\\[Serial\\]".
   SKIP="${SKIP:-}"
   FOCUS="${FOCUS:-}"
   LABEL_FILTER="${LABEL_FILTER:-}"
@@ -255,10 +264,12 @@ run_tests() {
   # if we set PARALLEL=true, skip serial tests set --ginkgo-parallel
   if [ "${PARALLEL:-false}" = "true" ]; then
     export GINKGO_PARALLEL=y
-    if [ -z "${SKIP}" ]; then
-      SKIP="\\[Serial\\]"
-    else
-      SKIP="\\[Serial\\]|${SKIP}"
+    if [ -z "${LABEL_FILTER}" ]; then
+      if [ -z "${SKIP}" ]; then
+        SKIP="\\[Serial\\]"
+      else
+        SKIP="\\[Serial\\]|${SKIP}"
+      fi
     fi
   fi