Converter container leaves defunct process

The converter pod calls some command-line tools to perform the conversions. These calls are wrapped by a Xvfb script which is required by the underlying CLI. This is the behavior of the converter pod since the beginning of ARender Docker Images.

This could lead to serious issues in production, for instance, the underlying server has a limited number of process to allocate, filling the stack of processes with defunct processes will lead at some point to a resource issue and will break/block correct behavior and further deployment on this node.

The reaping should be handled correctly to avoid this kind of issue.