cosmetic: rename conn_fsm "bump" event to "release_when_unused"

The naming of "bump" was short and made sense to me at the time of writing, but
it is keeping pretty much everyone else at a distance, no-one intuitively gets
what it is supposed to mean.

Clarify by renaming to "release_when_unused".

Adjust test expectations.

Change-Id: I4dcc55f536f63b13a3da29fff1df5fe16751f83a
14 files changed