Stop SYNTHESE at startup if server port is already used

• display a message and quit instead of following behaviour :

DEBUG # 2019/05/13 14:02:35.657457000 # HTTP_51924 # Thread ended for thread id 7f2d64cd9700
WARN  # 2019/05/13 14:02:35.657508000 # HTTP_51919 # Thread restarted with id 7f2d64cd9700
DEBUG # 2019/05/13 14:02:35.657610000 # HTTP_51920 # Starting thread 7f2d644d8700 - description : HTTP_51925
WARN  # 2019/05/13 14:02:35.657664000 # HTTP_51920 # Thread restarted with id 7f2d644d8700
DEBUG # 2019/05/13 14:02:35.657678000 # HTTP_51925 # Thread ended for thread id 7f2d644d8700
DEBUG # 2019/05/13 14:02:35.657746000 # HTTP_51921 # Starting thread 7f2d610c7700 - description : HTTP_51926
DEBUG # 2019/05/13 14:02:35.657785000 # HTTP_51921 # Thread ended for thread id 7f2d610c7700
WARN  # 2019/05/13 14:02:35.657817000 # HTTP_51921 # Thread restarted with id 7f2d610c7700
DEBUG # 2019/05/13 14:02:35.657873000 # HTTP_51926 # Starting thread 7f2d618c8700 - description : HTTP_51927
WARN  # 2019/05/13 14:02:35.657919000 # HTTP_51926 # Thread restarted with id 7f2d618c8700
DEBUG # 2019/05/13 14:02:35.657946000 # HTTP_51927 # Thread ended for thread id 7f2d618c8700
DEBUG # 2019/05/13 14:02:35.658034000 # HTTP_51923 # Starting thread 7f2d610c7700 - description : HTTP_51928
WARN  # 2019/05/13 14:02:35.658086000 # HTTP_51923 # Thread restarted with id 7f2d610c7700
DEBUG # 2019/05/13 14:02:35.658102000 # HTTP_51928 # Thread ended for thread id 7f2d610c7700
DEBUG # 2019/05/13 14:02:35.658174000 # HTTP_51924 # Starting thread 7f2d608c6700 - description : HTTP_51929
DEBUG # 2019/05/13 14:02:35.658222000 # HTTP_51929 # Thread ended for thread id 7f2d608c6700
WARN  # 2019/05/13 14:02:35.658252000 # HTTP_51924 # Thread restarted with id 7f2d608c6700
DEBUG # 2019/05/13 14:02:35.658304000 # HTTP_51929 # Starting thread 7f2d65ffb700 - description : HTTP_51930
WARN  # 2019/05/13 14:02:35.658348000 # HTTP_51929 # Thread restarted with id 7f2d65ffb700
DEBUG # 2019/05/13 14:02:35.658375000 # HTTP_51930 # Thread ended for thread id 7f2d65ffb700
DEBUG # 2019/05/13 14:02:35.658436000 # HTTP_51922 # Starting thread 7f2d608c6700 - description : HTTP_51931
DEBUG # 2019/05/13 14:02:35.658472000 # HTTP_51922 # Thread ended for thread id 7f2d608c6700
WARN  # 2019/05/13 14:02:35.658494000 # HTTP_51922 # Thread restarted with id 7f2d608c6700
DEBUG # 2019/05/13 14:02:35.658550000 # HTTP_51931 # Starting thread 7f2d64cd9700 - description : HTTP_51932
WARN  # 2019/05/13 14:02:35.658592000 # HTTP_51931 # Thread restarted with id 7f2d64cd9700
DEBUG # 2019/05/13 14:02:35.658624000 # HTTP_51932 # Thread ended for thread id 7f2d64cd9700
DEBUG # 2019/05/13 14:02:35.658678000 # HTTP_51928 # Starting thread 7f2d608c6700 - description : HTTP_51933
DEBUG # 2019/05/13 14:02:35.658716000 # HTTP_51928 # Thread ended for thread id 7f2d608c6700
WARN  # 2019/05/13 14:02:35.658753000 # HTTP_51928 # Thread restarted with id 7f2d608c6700
DEBUG # 2019/05/13 14:02:35.658841000 # HTTP_51925 # Starting thread 7f2d610c7700 - description : HTTP_51934
DEBUG # 2019/05/13 14:02:35.658872000 # HTTP_51925 # Thread ended for thread id 7f2d610c7700
WARN  # 2019/05/13 14:02:35.658894000 # HTTP_51925 # Thread restarted with id 7f2d610c7700
DEBUG # 2019/05/13 14:02:35.658948000 # HTTP_51934 # Starting thread 7f2d667fc700 - description : HTTP_51935
WARN  # 2019/05/13 14:02:35.658989000 # HTTP_51934 # Thread restarted with id 7f2d667fc700
DEBUG # 2019/05/13 14:02:35.659023000 # HTTP_51935 # Thread ended for thread id 7f2d667fc700
DEBUG # 2019/05/13 14:02:35.659076000 # HTTP_51927 # Starting thread 7f2d610c7700 - description : HTTP_51936
WARN  # 2019/05/13 14:02:35.659130000 # HTTP_51927 # Thread restarted with id 7f2d610c7700
DEBUG # 2019/05/13 14:02:35.659147000 # HTTP_51936 # Thread ended for thread id 7f2d610c7700
DEBUG # 2019/05/13 14:02:35.659221000 # HTTP_51932 # Starting thread 7f2d618c8700 - description : HTTP_51937
DEBUG # 2019/05/13 14:02:35.659243000 # HTTP_51932 # Thread ended for thread id 7f2d618c8700
WARN  # 2019/05/13 14:02:35.659274000 # HTTP_51932 # Thread restarted with id 7f2d618c8700
DEBUG # 2019/05/13 14:02:35.659363000 # HTTP_51933 # Starting thread 7f2d64cd9700 - description : HTTP_51938
WARN  # 2019/05/13 14:02:35.659416000 # HTTP_51933 # Thread restarted with id 7f2d64cd9700
DEBUG # 2019/05/13 14:02:35.659442000 # HTTP_51938 # Thread ended for thread id 7f2d64cd9700
DEBUG # 2019/05/13 14:02:35.659542000 # HTTP_51930 # Starting thread 7f2d608c6700 - description : HTTP_51939
DEBUG # 2019/05/13 14:02:35.659597000 # HTTP_51939 # Thread ended for thread id 7f2d608c6700