SupportLeanbackShowcase: bring gradle, build tools, lib up to date
am: 15f5a3351f

* commit '15f5a3351ff79b37d0f899e3ae9ac1b535306fe3':
  SupportLeanbackShowcase: bring gradle, build tools, lib up to date

Change-Id: I9922a3a645cdce7908ce342761d2ac997ddb8720