Keystore 2.0: Untangle mutex dependencies in add_auth_token.

Some mutexes on the add_auth_token path were more dependent on one
another than necessary. This could lead to a chain were add_auth_token
would block on waiting for a time stamp token, which in turn could stall
the execution for seconds.

Also fix some comments.

Bug: 183676395
Test: N/A
Change-Id: I5c6ae1e47fe232ea9954497108f807bbcd37fef7
3 files changed