Build leanback with Gradle.

Change-Id: Id3a2664149aa18b865957dca6aa8d44e3c062e62
diff --git a/settings.gradle b/settings.gradle
index 2104257..b92434f 100644
--- a/settings.gradle
+++ b/settings.gradle
@@ -18,3 +18,6 @@
 
 include ':support-v13'
 project(':support-v13').projectDir = new File(rootDir, 'v13')
+
+include ':support-leanback-v17'
+project(':support-leanback-v17').projectDir = new File(rootDir, 'v17/leanback')