Include android-gts/lib folder in android-gts.zip

Some gts tests such as JniUncompressGtsTestCases need native libraries
and those should be located under android-gts/lib.

Test: confirmed that the android-gts.zip includes lib folder
Bug: 186595833
Change-Id: I7d0605d0aff861059e3788630585e9ba412f9cac