docker (libervia_cont): added a "status" command: - if libervia container is not running, it exits with error code 1 - if libervia container is running but no server is launched, it exits with error code 2 - if libervia container is running and server is launcher, it exits with error code 0 (success) server detection is done by doing a simple grep on logs, that's not perfectly reliable (ports can be changed in configuration, even if that doesn't really make sense in Docker context) but should be good enough for this purpose.