Common: Replace ExecutionBarrier with std::promise and std::future

* std::promise and std::future are able to achieve the same
  functionalities of ExecutionBarrier with extra flexibility
* Replace "_barrier" with "_promise" in system/bt/common

Bug: 110303473
Fixes: 112159657
Test: mm -j40, unit test
Change-Id: I2a420bbf16bf92e4b3dd256d9f23480fc2be7be1