Changed for Android Gradle plugin 0.9

See the http://tools.android.com/tech-docs/new-build-system/migrating_to_09

However, I'm modifying build.gradle to below for IntelliJ IDEA 13.1.1, because it seems not support 0.9 yet.

build.gradle
```
classpath 'com.android.tools.build:gradle:0.8.+'
...
    instrumentTest {
```