Update kokoro bazel runner for v4.

.kokoro

@@ -20,7 +20,35 @@ set -e
 # Display commands to stderr.
 set -x
 
-KOKORO_RUNNER_VERSION="v3.*"
+KOKORO_RUNNER_VERSION="v4.*"
+
+POSITIONAL=()
+while [[ $# -gt 0 ]]; do
+  key="$1"
+
+  case $key in
+  -v|--verbose)
+    VERBOSE_OUTPUT="1"
+    shift
+    ;;
+  *)
+    POSITIONAL+=("$1")
+    shift
+    ;;
+  esac
+done
+set -- "${POSITIONAL[@]}" # restore positional parameters
+
+if [ -n "$KOKORO_BUILD_NUMBER" ]; then
+  # Always enable verbose output on kokoro runs.
+  VERBOSE_OUTPUT=1
+fi
+
+if [ -n "$VERBOSE_OUTPUT" ]; then
+  # Display commands to stderr.
+  set -x
+  verbosity_args="-v"
+fi
 
 if [ ! -d .kokoro-ios-runner ]; then
   git clone https://github.com/material-foundation/kokoro-ios-runner.git .kokoro-ios-runner
@@ -33,6 +61,6 @@ TAG=$(git tag --sort=v:refname -l "$KOKORO_RUNNER_VERSION" | tail -n1)
 git checkout "$TAG" > /dev/null
 popd
 
-./.kokoro-ios-runner/bazel.sh test //:UnitTests 8.1.0
+./.kokoro-ios-runner/bazel.sh test //:UnitTests --min-xcode-version 8.1.0 $verbosity_args
 
 echo "Success!"