Make shell bugreport file names consistent with dumpstate

Since bugreport API workflow will be replacing old workflow of directly
starting dumpstate, we aim that the resulting file names be the same as
the users are used to the old file names (that dumpstate used to decide).

Bug:126862297
Test: * Build and flash to the device
      * Turn on Settings feature flag to use the bugreport API
      * Take interactive and full bugreports
      * Output file names same as before

Change-Id: I24d800e26a8cc4f739038ac0f27da13bd83f7f47