Fix issues during cleanup stage of the Bluetooth stack

 * Moved free-ing of bta_av_cb timers from the init function
   to the cleanup stage.
 * Changed the usage of btif_jni_disassociate() so it is called
   synchronously. Its previous usage was complicated -
   the function was called asynchronously on a different thread,
   and we had to wait on a future for its completion.
 * Renamed function btif_shutdown_bluetooth() to
   btif_cleanup_bluetooth() to represent better its purpose.
   Similarly, bte_main_shutdown() is renamed to bte_main_cleanup()

Also:
 * Removed function btif_init_fail(), because it is not used.
 * Updated an error log message inside function
   btif_in_execute_service_request() so the log information
   is accurate and more useful.
 * Updated the log messages related to the lifecycle of a module
   in btcore/src/module.c

Bug: 26982349
Change-Id: Icd6f159d993bdb9c8ef09bfb5b1386b3d6ea4ff2