Fix bierman02 ListenerAdapter memory leak

Storing notifications in a field causes them to be retained for
longer than needed. Pass them as arguments, fixing the leak and
making the adapter stateless.

Change-Id: I8cfb335db0ad21d37d5cce79e6fdbe31efc1ab8a
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>