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

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

Change-Id: I49d8310f1a2a0cce83ab1bc55b6d34b3c9848114