[automerger] Fix probable prime confidence calculations. am: 91719e3c1b am: b2a687151e am: b56197f5fd am: 630facd786 am: 77321115ab am: 87804b8da9
am: 883aa9d8f8

Change-Id: I845c8716a1f37a5d6a74ff4779d98704313a41bd