Add kotlin-stdlib-jdk8 when using Kotlin

kotlin-stdlib-jdk8 contains extensions to the Kotlin standard library
for use when targeting Java language level 8.

Test: m checkbuild
Change-Id: Iac5f977f9080d8e0e2402b08a992a93c909744e9
diff --git a/java/testing.go b/java/testing.go
index 1be3768..22831c9 100644
--- a/java/testing.go
+++ b/java/testing.go
@@ -44,6 +44,8 @@
 		"core.current.stubs",
 		"core.platform.api.stubs",
 		"kotlin-stdlib",
+		"kotlin-stdlib-jdk7",
+		"kotlin-stdlib-jdk8",
 		"kotlin-annotations",
 	}