To sum up, for those don't know how to import package in build.gradle(like me), use the following buildTypes,
buildTypes {
      release {
        signingConfig signingConfigs.release
        applicationVariants.all { variant ->
            def file = variant.outputFile
            def manifestParser = new com.android.builder.core.DefaultManifestParser()
            variant.outputFile = new File(file.parent, file.name.replace(".apk", "-" + manifestParser.getVersionName(android.sourceSets.main.manifest.srcFile) + ".apk")) 
        }
    }       
}
===== EDIT =====
If you set your versionCode and versionName in your build.gradle file like this: 
defaultConfig {
    minSdkVersion 15
    targetSdkVersion 19
    versionCode 1
    versionName "1.0.0"
}
You should set it like this:
buildTypes {   
        release {
            signingConfig signingConfigs.releaseConfig
            applicationVariants.all { variant ->
                def file = variant.outputFile
                variant.outputFile = new File(file.parent, file.name.replace(".apk", "-" + defaultConfig.versionName + ".apk"))
            }
        }
}
====== EDIT with Android Studio 1.0 ======
If you are using Android Studio 1.0, you will get an error like this:
Error:(78, 0) Could not find property 'outputFile' on com.android.build.gradle.internal.api.ApplicationVariantImpl_Decorated@67e7625f.
You should change the build.Types part to this:
buildTypes {
        release {
            signingConfig signingConfigs.releaseConfig
            applicationVariants.all { variant ->
                variant.outputs.each { output ->
                    output.outputFile = new File(output.outputFile.parent, output.outputFile.name.replace(".apk", "-" + defaultConfig.versionName + ".apk"))
                }
            }
        }
    }