Using the healthcheck middleware as a filter is deprecated and
the middleware should be used as an application[1].
[1] 6feaa13610c450c8486f969703768db5319b4846
This change updates definition and usage of the healthcheck middleware
accordingly to avoid the following deprecation warning.
DeprecationWarning: Using function/method 'Healthcheck.factory()' is
deprecated: The healthcheck middleware must now be configured as
an application, not as a filter.
Change-Id: Ie81140d3b03c315f0a057d2f59754ee14dac539c
ce217a287c