Uncompress .so files before signing the apk.

- In uncompress-shared-libs we may strip .so files not for the current
  TARGET_ARCH. So we need to strip first and then sign the apk.
- For PRESIGNED apks, make sure we don't strip the .so files even if
   they are "fat".

Bug: 21571418
Bug: 8076853
Change-Id: Ifd1193dda0c2cd52ac148064ce5a32bcdd03f75c