bin: add --check-liveliness support

Refactored the healt checking plugin creating
a shared module for checking the engine liveliness.
Adedd --check-liveliness support calling the new module.

Change-Id: If146459d62815dcf030fcd151b61faddb6af8be9
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>