Set the math.randomseed value in nse_main.lua on behalf of scripts.

Since Lua uses the C rand and srand functions, which have a static
seed for the entire program, we don't want scripts doing this themselves.

scripts/dhcp-discover.nse

@@ -82,9 +82,6 @@ end
 --end
 
 local function go(host, port)
-	-- We're going to need some low quality random numbers
-	math.randomseed(os.time())
-
 	-- Set up a fake host for prerule
 	if(not(host)) then
 		host = {}

scripts/dns-fuzz.nse

@@ -280,7 +280,6 @@ function corruptAndSend (host, port, query)
 end
 
 action = function(host, port)
-     math.randomseed(os.time())
      local endT
      local timelimit, err
      local retStr

scripts/nping-brute.nse

@@ -180,7 +180,6 @@ Driver =
 }
 
 action = function(host, port)
-	math.randomseed(nmap.clock())
 	local engine = brute.Engine:new(Driver, host, port)
 	engine.options.firstonly = true
 	engine.options:setOption("passonly", true)

scripts/oracle-enum-users.nse

@@ -79,13 +79,6 @@ local function get_random_string(length, set)
 
 	local str = ""
 
-	-- Seed the random number, if we haven't already
-	if (not(nmap.registry.oracle_enum_users) or not(nmap.registry.oracle_enum_users.seeded)) then
-		math.randomseed(os.time())
-		nmap.registry.oracle_enum_users = {}
-		nmap.registry.oracle_enum_users.seeded = true
-	end
-
 	for i = 1, length, 1 do
 		local random = math.random(#set)
 		str = str .. string.sub(set, random, random)

scripts/sip-brute.nse

@@ -73,7 +73,6 @@ Driver = {
 -- was successful which makes it impossible to tell successfull logins
 -- from non-existing accounts apart.
 local function checkBadUser(host, port)
-	math.randomseed( os.time() )
 	local user = "baduser-" .. math.random(10000)
 	local pass = "badpass-" .. math.random(10000)
 	local helper = sip.Helper:new(host, port, { expires = 0 })
@@ -103,4 +102,4 @@ action = function(host, port)
 	local engine = brute.Engine:new(Driver, host, port)
 	local status, result = engine:start()
 	return result
-end
+end

scripts/smb-brute.nse

@@ -172,13 +172,6 @@ local function get_random_string(length, set)
 
 	local str = ""
 
-	-- Seed the random number, if we haven't already
-	if not nmap.registry.smbbrute or not nmap.registry.smbbrute.seeded then
-		math.randomseed(os.time())
-		nmap.registry.smbbrute = {}
-		nmap.registry.smbbrute.seeded = true
-	end
-
 	for i = 1, length, 1 do
 		local random = math.random(#set)
 		str = str .. string.sub(set, random, random)

scripts/smb-psexec.nse

@@ -693,7 +693,6 @@ local function get_config(host, config)
 	elseif(nmap.registry.args.key) then
 		config.key = nmap.registry.args.key
 	else
-		math.randomseed( os.time() )
 		config.key = ""
 		for i = 1, 127, 1 do
 			config.key = config.key .. string.char(math.random(0x20, 0x7F))