Add a second_chance on cmd_use

This is a weak attempt to solve a race condition between modules loading
and cmd_use being fired. Upon startup, saved configurations, running
resource scripts, and running commands will sometimes jump ahead of the
module loading procedure.

I have not discovered where the race actually is and how to cause the
race to happen. However, the timing seems to be fairly close to a second;
by waiting three seconds after trying use again, we seem to be in the
clear, at least according to testing.

Fixes #4549, but better solutions are welcome!

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

@@ -2418,9 +2418,15 @@ class Core
     mod_name = args[0]
 
     begin
-      if ((mod = framework.modules.create(mod_name)) == nil)
-        print_error("Failed to load module: #{mod_name}")
-        return false
+      mod = framework.modules.create(mod_name)
+      if mod.nil?
+        # Try one more time; see #4549
+        sleep 3
+        mod = framework.modules.create(mod_name)
+        if mod.nil?
+          print_error("Failed to load module: #{mod_name}")
+          return false
+        end
       end
     rescue Rex::AmbiguousArgumentError => info
       print_error(info.to_s)