To reproduce:

1. Download attached project "AndroidTest.zip"
2. Open Command Prompt
3. Write this line "\path\to\Unity.exe" -batchMode -projectPath "\path\to\this\project" -quit -executeMethod Builder.Build -buildTarget Android and execute it
4. Open Task Manager, find there Windows Command Processor and expand it
5. Wait until Build is complete
6. Observe that after a build is complete, the Java.exe process that executed Gradle remains running

Notes:
- This process is holding on to several file handles (including the Unity log file) and consumes a lot of memory
- If you try to Build project in Unity Editor, there will also be the Java.exe process that executed Gradle running, but after you close Unity Editor, it will be terminated

Reproduced on Unity 2018.2.3f1, 2018.2.6f1 and 2018.3.0a11
Not reproduced on Unity 2018.1.9f2 and 2018.2.2f1 (c18cef34cbcd)
Regression on Unity 2018.2.3f1 (1431a7d2ced7)