Reduce time between attempts, fix style, unless/if

In order to avoid wasting too much time sleeping between attempts, just
sleep 0.1 seconds and retry 300 times.

Also fixed a style bug on line 2565, use `return false unless mod`
instead of `return false if mod.nil?`

[See rapid7#4340] [See rapid7#4615]

lib/msf/ui/console/command_dispatcher/core.rb

@@ -102,10 +102,10 @@ class Core
   DISCLOSURE_DATE_FORMAT = "%Y-%m-%d"
 
   # Sleep time in seconds between module use retries (see #4340)
-  CMD_USE_TIMEOUT = 1
+  CMD_USE_TIMEOUT = 0.1
 
   # Total retry attempts before giving up on using a module (see #4340)
-  CMD_USE_ATTEMPTS = 30
+  CMD_USE_ATTEMPTS = 300
 
   # Returns the list of commands supported by this command dispatcher
   def commands
@@ -2544,9 +2544,9 @@ def cmd_use(*args)
 
     # Try to create an instance of the supplied module name
     mod_name = args[0]
+    mod = nil
 
     begin
-      mod = nil
       CMD_USE_ATTEMPTS.times do
         mod = framework.modules.create(mod_name)
         break if mod
@@ -2562,7 +2562,7 @@ def cmd_use(*args)
       log_error("The supplied module name is ambiguous: #{$!}.")
     end
 
-    return false if (mod == nil)
+    return false unless mod
 
     # Enstack the command dispatcher for this module type
     dispatcher = nil