Tests: Add a health check utility program

Tests: Add a health check utility program

The health_check program is a simple utility to query the health
status of the different threads of the sessiond.

Sample output:

> ./health_check
Health check cmd: 0
Health check app. manage: 0
Health check app. registration: 0
Health check kernel: 0
Health check consumer: 0

The return code is encoded to indicate which thread has failed.

Signed-off-by: Christian Babeux <christian.babeux@efficios.com>
Signed-off-by: David Goulet <dgoulet@efficios.com>