set a system property indicated by a specified key and value.
prev = system_setproperty(key,value)
:prev a string previous value or [] : :key a string : :value a string :
Sets the system property indicated by the specified key.
Warning : change property with precaution.
`system_getproperty`_('myproperty')
system_setproperty('myproperty','hello')
`system_getproperty`_('myproperty')