Update to Gradle 3.2.

- Add gradle-3.1.bin.zip and gradle-api-3.2.jar (gradle-api-3.2.jar is
  generated using the gradleApi() method).

Test: cd tools && ./gradlew test
Change-Id: Ie0caa389b40a7fb0d3bd179d88cbdbb66561c67a
6 files changed