block mode fixes
1) -o rozofsmode=1 rozofsmount option was ignored. Block mode was could only
   be set through a rozodebug command
2) When block mode is set, only cache regulard file attributes, and not
   symbolink links and directories attributes
Use severe () and fatal() instead of ERRLOG and ERRFAT
kill STORIO before starting it
Before starting a STORIO instance the storaged launches the STORIO killer
just in case the previous STORIO is still running !!!