set general verbosity level
:param O:
:type O: None
:param 1:
:type 1: + Error
:param 2:
:type 2: + Warning
:param 3:
:type 3: + Info
:param 4:
:type 4: + Debug
:param NB:
:type NB: to add Debug verbosity to the log VERBOSITY_LEVEL has to be set to 4