Export proguard flags from static android libraries and aar prebuilts

Test: m Contacts, classes-proguard.jar has same contents
Test: rm -rf out; tapas Contacts; m
Change-Id: Id7a92fb2c44913bccbfcbeae127355b4de588e4d
Merged-In: Id7a92fb2c44913bccbfcbeae127355b4de588e4d
(cherry picked from commit 1417c177)