Use env variable

Author: dongjoon-hyun

dev/run-tests.py

@@ -363,7 +363,7 @@ def build_spark_assembly_sbt(extra_profiles, checkstyle=False):
     if checkstyle:
         run_java_style_checks(build_profiles)
 
-    if test_env != "amplab_jenkins":
+    if not os.environ.get("AMPLAB_JENKINS"):
         build_spark_unidoc_sbt(extra_profiles)