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/plugin_test.go b/java/plugin_test.go
index dc29b1c..95f4aca 100644
--- a/java/plugin_test.go
+++ b/java/plugin_test.go
@@ -19,6 +19,7 @@
 )
 
 func TestNoPlugin(t *testing.T) {
+	t.Parallel()
 	ctx, _ := testJava(t, `
 		java_library {
 			name: "foo",
@@ -43,6 +44,7 @@
 }
 
 func TestPlugin(t *testing.T) {
+	t.Parallel()
 	ctx, _ := testJava(t, `
 		java_library {
 			name: "foo",
@@ -82,6 +84,7 @@
 }
 
 func TestPluginGeneratesApi(t *testing.T) {
+	t.Parallel()
 	ctx, _ := testJava(t, `
 		java_library {
 			name: "foo",