Correctly handle HAL death

In the presence of multiple sessions, we would modify the
mActiveSessions list while iterating it, causing a runtime exception.
This has not been observed before, since we never had more than one
session.

In addition, unified the exception used to convey a dead module.

Test: Killed STHAL process and observed recovery.
Bug: 163865561
Change-Id: Ib5c5f81463d51e0f1bacae3a689fd9c8515cecc9