Run TestClasspath subtests in parallel

Call t.Parallel() to make the subtests of TestClasspath run in
parallel, which drops the runtime from 12 seconds to 1.7 seconds.

Test: TestClasspath
Flag: EXEMPT refactor
Change-Id: Id2194f6b5f925b480280e9cf8da5d5767a467430

java/sdk_test.go

@@ -388,7 +388,9 @@ func TestClasspath(t *testing.T) {
 		},
 	}
 
+	t.Parallel()
 	t.Run("basic", func(t *testing.T) {
+		t.Parallel()
 		testClasspathTestCases(t, classpathTestcases, false)
 	})
 
@@ -404,6 +406,7 @@ func testClasspathTestCases(t *testing.T, classpathTestcases []classpathTestCase
 		}
 
 		t.Run(testcase.name, func(t *testing.T) {
+			t.Parallel()
 			moduleType := "java_library"
 			if testcase.moduleType != "" {
 				moduleType = testcase.moduleType