Be less aggressive when not resuming top activity

The previous fix for keeping activities from running on startup,
ag/363992, was keeping the home task from launching when the
keyguard should have allowed it.

This fix permits the home activity to launch in such situations.

Fixes bug 10916877.

Change-Id: I429f0d5a13e06a247b9b6b7241f9a3514044c371