How to reproduce:
1. Open the attached project "GradleAndroidRes.zip"
2. Open Build Settings and select Android platform
3. Select "Gradle" or "Internal" as the build system
4. Build for Android
5. Build fails with duplicated error message

Actual result: You get two identical error messages
Expected result: Error message should be reported once

Reproducible: 5.5.0b1, 5.5.0f2, 5.6.0a5
Not reproducible: 5.4.3p3 (Internal build system),
Gradle introduced in Unity 5.5