Dynamic servers feature is now judged to be stable enough. Remove the
experimental-mode requirement for "add/del server" commands. This should
facilitate dynamic servers adoption.
Create a regtest for the 'track' keyword support by dynamic servers.
First checks are executed to ensure that tracking cannot be activated on
non-check server or dynamic servers.
Then, 3 scenarii are written to ensure that the deletion of a dynamic
server with track is properly handled and other servers in the track
chain are properly maintained.