SignApk: setLevel(9) should be called on APKs and not OTAs.

Change-Id: I3ca668461b838a415ecedb81a995ad530869b10b
SignApk: perform the whole file signature in a single streaming pass.

Change-Id: Ib56918adad067940a8e14c41c61b42b953504183

Author:    Koushik Dutta <koushd@gmail.com>