Switch to correct runfiles directory when running python test on Windows

py_test cannot find it's data file at runtime. The reason is it's
running in a wrong directory.

The test directory is set to runfiles directory by test-setup.sh, but on
Windows, python binary unzip itself to another temp directory which
test-setup.sh doesn't know.

So let the python stub template switch to the correct runfiles directory
if RUN_UNDER_RUNFILES = 1

Fixed https://github.com/bazelbuild/bazel/issues/3134

Change-Id: If5dbee811330372d86484ebd871ea55d84bc29a8
PiperOrigin-RevId: 158299041
diff --git a/src/main/java/com/google/devtools/build/lib/exec/StandaloneTestStrategy.java b/src/main/java/com/google/devtools/build/lib/exec/StandaloneTestStrategy.java
index 58aed28..b3100c2 100644
--- a/src/main/java/com/google/devtools/build/lib/exec/StandaloneTestStrategy.java
+++ b/src/main/java/com/google/devtools/build/lib/exec/StandaloneTestStrategy.java
@@ -72,6 +72,7 @@
           .put("PYTHON_RUNFILES", TestPolicy.RUNFILES_DIR)
           .put("RUNFILES_DIR", TestPolicy.RUNFILES_DIR)
           .put("TEST_TMPDIR", TestPolicy.TEST_TMP_DIR)
+          .put("RUN_UNDER_RUNFILES", "1")
           .build();
 
   public static final TestPolicy DEFAULT_LOCAL_POLICY = new TestPolicy(ENV_VARS);