Don't dexpreopt or strip java_test modules

I6bb2c971cee65d2338839753aa0d84939f335b1b accidentally caused
java_test modules to be dexpreopted and possibly stripped.

Test: dexpreopt_test.go
Change-Id: Ida8f046c509c97e38bd3bce66944d32f01530db4

java/dexpreopt_test.go

@@ -82,6 +82,15 @@ func TestDexpreoptEnabled(t *testing.T) {
 				}`,
 			enabled: false,
 		},
+		{
+			name: "java test",
+			bp: `
+				java_test {
+					name: "foo",
+					srcs: ["a.java"],
+				}`,
+			enabled: false,
+		},
 		{
 			name: "android test",
 			bp: `

java/java.go

@@ -1601,6 +1601,7 @@ func TestFactory() android.Module {
 		&module.testProperties)
 
 	module.Module.properties.Installable = proptools.BoolPtr(true)
+	module.Module.dexpreopter.isTest = true
 
 	InitJavaModule(module, android.HostAndDeviceSupported)
 	return module