verify: pick relevant lines from verify-golangci-lint.sh as failure message

When sh2ju.sh was called to generate the junit_verify.xml, it used to include
the entire output of a failed script twice: once as failure message, once as
log output.

This output can be large and often the actual failure isn't near the top, but
rather at the end or (in the case of the different golangci-lint invocations)
embedded in the log. This makes them hard to see at a glance when looking at
the Prow result page for a job.

Now a verify script can prefix relevant lines with "ERROR: " and then only
those lines are used as failure message in JUnit, without that prefix.

That string was chosen because Prow itself also then picks up those lines when
viewing the entire build log and it is unlikely that some script prints such
lines when they are not meant to be part of the failure.

If some script outputs no such lines, "see stderr for details" is used as
failure message. This is better than before because it avoids the redundancy.

hack/verify-golangci-lint.sh

@@ -97,6 +97,19 @@ if [ "${golangci_config}" ]; then
     golangci+=(--config="${golangci_config}")
 fi
 
+# Below the output of golangci-lint is going to be piped into sed to add
+# a prefix to each output line. This helps make the output more visible
+# in the Prow log viewer ("error" is a key word there) and ensures that
+# only those lines get included as failure message in a JUnit file
+# by "make verify".
+#
+# The downside is that the automatic detection whether to colorize output
+# doesn't work anymore, so here we force it ourselves when connected to
+# a tty.
+if tty -s; then
+    golangci+=(--color=always)
+fi
+
 if [ "$base" ]; then
     # Must be a something that git can resolve to a commit.
     # "git rev-parse --verify" checks that and prints a detailed
@@ -139,15 +152,15 @@ res=0
 run () {
   if [[ "${#targets[@]}" -gt 0 ]]; then
     echo "running ${golangci[*]} ${targets[*]}" >&2
-    "${golangci[@]}" "${targets[@]}" >&2 || res=$?
+    "${golangci[@]}" "${targets[@]}" 2>&1 | sed -e 's;^;ERROR: ;' >&2 || res=$?
   else
     echo "running ${golangci[*]} ./..." >&2
-    "${golangci[@]}" ./... >&2 || res=$?
+    "${golangci[@]}" ./... 2>&1 | sed -e 's;^;ERROR: ;' >&2 || res=$?
     for d in staging/src/k8s.io/*; do
       MODPATH="staging/src/k8s.io/$(basename "${d}")"
       echo "running ( cd ${KUBE_ROOT}/${MODPATH}; ${golangci[*]} --path-prefix ${MODPATH} ./... )"
       pushd "${KUBE_ROOT}/${MODPATH}" >/dev/null
-        "${golangci[@]}" --path-prefix "${MODPATH}" ./... >&2 || res=$?
+        "${golangci[@]}" --path-prefix "${MODPATH}" ./... 2>&1 | sed -e 's;^;ERROR: ;' >&2 || res=$?
       popd >/dev/null
     done
   fi