ScreenshotTestSample with Gradle Manged Devices and several shards generates screenshots for last shard only

[sergio-sastre]

If I run
./gradlew nexusOneApi30DebugAndroidTest -Pandroid.experimental.androidTest.numManagedDeviceShards=2

I see the following in the terminal:

Task :app:nexusOneApi30DebugAndroidTest
Starting 4 tests on nexusOneApi30_0
Starting 2 tests on nexusOneApi30_1

And then in the build folder only the screenshots for shard 1 are generated: those from shard 1 are missing:

Remarks:
I've executed the command several times. Sometimes the first shard is assigned 2 tests, and the second 4, sometimes the first is assigned 4 and the second one 2. In both cases, only the screenshots of the second shard are generated in the corresponding folder

Expected:
The screenshots of all shards are generated in the corresponding folder