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

java/testing.go

@@ -44,6 +44,8 @@ func GatherRequiredDepsForTest() string {
 		"core.current.stubs",
 		"core.platform.api.stubs",
 		"kotlin-stdlib",
+		"kotlin-stdlib-jdk7",
+		"kotlin-stdlib-jdk8",
 		"kotlin-annotations",
 	}