ITrigEventLoopMgr: add prepareForStart method
Add a new ITrigEventLoopMgr::prepareForStart
method to the
HltEventLoopMgr
that is being called by the Psc
before calling the
start method of the ApplicationMgr
. This will allow the EventLoopMgr to
setup anything that may be required during start
(e.g. setting up
a partial EventContext, ATR-21331).
This MR replaces !35257 (closed).
Also cleanup some duplicate error messages.