Set sdk_version "current" in test package

java_library com.android.test.libs.product is located in product
partition, but its sdk_version isn't set. And it will be forbidden.

So set sdk_version "current"

Test: mma
Bug: 137908189
Change-Id: I3f5a164703f0e5a1f7d43b9f28cda7fa99033186