Pin support libraries to Java 1.7 so they can be used with dx

The .jar artifacts must contain v51 class files to prevent them
being rejected by dx.

Bug: 26753820
Bug: 27353172
Bug: 27338966
(cherry-picked from commit e1cd5a1f80010eece43cb4608505fd39f4832c00)

Change-Id: I04f5f32aea99fdc680305a273bae3bc3fff884c5
21 files changed