Add t.Parallel() to java tests

Speeds up go test ./java from 32 seconds to 9 seconds.

Test: go test ./java
Change-Id: I4c6640e787c0744c6dfda03b7382839b452e24cf
diff --git a/java/system_modules_test.go b/java/system_modules_test.go
index b05b0e4..b7a99b5 100644
--- a/java/system_modules_test.go
+++ b/java/system_modules_test.go
@@ -51,6 +51,7 @@
 `)
 
 func TestJavaSystemModules(t *testing.T) {
+	t.Parallel()
 	result := android.GroupFixturePreparers(prepareForJavaTest, addSourceSystemModules).RunTest(t)
 
 	// check the existence of the source module
@@ -78,6 +79,7 @@
 `)
 
 func TestJavaSystemModulesImport(t *testing.T) {
+	t.Parallel()
 	result := android.GroupFixturePreparers(prepareForJavaTest, addPrebuiltSystemModules).RunTest(t)
 
 	// check the existence of the renamed prebuilt module
@@ -90,6 +92,7 @@
 }
 
 func TestJavaSystemModulesMixSourceAndPrebuilt(t *testing.T) {
+	t.Parallel()
 	result := android.GroupFixturePreparers(
 		prepareForJavaTest,
 		addSourceSystemModules,
@@ -114,6 +117,7 @@
 }
 
 func TestMultipleSystemModulesPrebuilts(t *testing.T) {
+	t.Parallel()
 	bp := `
 		// an rdep
 		java_library {