Fix: change health poll update to entry/exit calls

Fix: change health poll update to entry/exit calls

It adds a better semantic to the code flow. Furthermore, the current
counter of the health state is now validated raising an assert() if the
value is unexepected.

Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>