Make unit test runs MUCH faster

Running tests rebuilds almost everything.  Most unit tests do not need to be
rebuilt.  This installs test artifacts and makes subsequent test runs as much
as 6x faster.  I saw pkg/apiserver tests drop from 30+ seconds to 5 seconds.

hack/make-rules/test.sh

@@ -194,6 +194,12 @@ runTests() {
   # command, which is much faster.
   if [[ ! ${KUBE_COVER} =~ ^[yY]$ ]]; then
     kube::log::status "Running tests without code coverage"
+    # `go test` does not install the things it builds. `go test -i` installs
+    # the build artifacts but doesn't run the tests.  The two together provide
+    # a large speedup for tests that do not need to be rebuilt.
+    go test -i "${goflags[@]:+${goflags[@]}}" \
+      ${KUBE_RACE} ${KUBE_TIMEOUT} "${@+${@/#/${KUBE_GO_PACKAGE}/}}" \
+     "${testargs[@]:+${testargs[@]}}"
     go test "${goflags[@]:+${goflags[@]}}" \
       ${KUBE_RACE} ${KUBE_TIMEOUT} "${@+${@/#/${KUBE_GO_PACKAGE}/}}" \
      "${testargs[@]:+${testargs[@]}}" \
@@ -220,8 +226,19 @@ runTests() {
   # separate files.
   # cmd/libs/go2idl/generator is fragile when run under coverage, so ignore it for now.
   # see: https://github.com/kubernetes/kubernetes/issues/24967
+  #
+  # `go test` does not install the things it builds. `go test -i` installs
+  # the build artifacts but doesn't run the tests.  The two together provide
+  # a large speedup for tests that do not need to be rebuilt.
   printf "%s\n" "${@}" | grep -v "cmd/libs/go2idl/generator"| xargs -I{} -n1 -P${KUBE_COVERPROCS} \
     bash -c "set -o pipefail; _pkg=\"{}\"; _pkg_out=\${_pkg//\//_}; \
+        go test -i ${goflags[@]:+${goflags[@]}} \
+          ${KUBE_RACE} \
+          ${KUBE_TIMEOUT} \
+          -cover -covermode=\"${KUBE_COVERMODE}\" \
+          -coverprofile=\"${cover_report_dir}/\${_pkg}/${cover_profile}\" \
+          \"${KUBE_GO_PACKAGE}/\${_pkg}\" \
+          ${testargs[@]:+${testargs[@]}}
         go test ${goflags[@]:+${goflags[@]}} \
           ${KUBE_RACE} \
           ${KUBE_TIMEOUT} \