Replace ndelay_off functions by io_set_block functions.

Using 'remove -P' cause issue due of the removed missing dependency for a service.
However, even if the graph displayed may not be strictly
exact for this case, a start command which required the missing dependencies
will be treat correctly as the system have trace of the
state of the dependencies graph for the entire system.
This is clearly ugly and a temporary fix. The graph function actually used will be dropped
in a near future due of the event features apparition.
Add STATE_FLAGS_MISSING flags

Review needed header files declaration and be clearer at variable name.

Add check target to handle test.

-wR can cause issue with notification readiness.

The fdholder will be freed to time. Let the shutdown algorithm handle it.

Fix unsupervision of the scandir avoiding remove inner daemon.
Do not crash if rc.shudown return a fail.
Fix signal to sent to the remaining service inside container.

Fix CONTAINER_HALTCMD value.

Avoid using it at 66 configuration file parse process.
Kernel parameters should not be part of the svscan process.
Only define strict mandatory variable at stage2 call.
Follow skarnet changes from s6-linux-init program.