Fix TrustAgent showing unclear string.

TrustAgents currently show the string "Device was locked manually" if
the trustagent times out, or if lockUser() was called. Changed to show a
more generic string, informing the user that they need to authenticate
with whatever credentials they have set up (instead of using the
trustagent).

Test: Test trustagent timeout, lockUser, verify string appears
Bug: 243710694
Change-Id: I96b113ab3ae63123782517339b0bdb3c6cdec2e2