Fix: Do not install health tests helper libraries

The libraries libhealthexit and libhealthstall should not be installed
on the user system. They are only useful for the health check tests.

Furthermore, when adding libraries to noinst_LTLIBRARIES, libtool will
only build these as static libraries (see [1] for a workaround). This is
fine for most use cases, but for the health tests, we _must_ have shared
libraries (the nature of the tests require LD_PRELOAD), hence we force
the build of a shared object.

Forcing shared object has the unfortunate side-effect of breaking builds
where configure was invoked with "--disable-shared" flag.  Instead of
failing badly, detect this flag and skip the health tests altogether.

noinst shared libs:
[1] - https://lists.gnu.org/archive/html/libtool/2008-06/msg00082.html

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