Optimized instrumentation listener handling

Some instrumentation listener lists may be modified while iterating
over the list to deliver an instrumentation event. Therefore the
previous implementation copied the list of listeners before starting
the iteration.

This new implementation only copies the list of instrumentation
listeners when the list is changed. Instances of the list are
reference counted using std::shared_ptr<>.

Change-Id: I1b84db1f2042836dc1110925243f49e5790156d6