Add logout page verification

Author: Jonathan Claudius

modules/exploits/multi/http/cisco_ssl_vpn_priv_esc.rb

@@ -107,7 +107,12 @@ def do_logout(cookie)
             'cookie' => cookie
           )
 
-    print_good("#{peer} - Logged out")
+    if res &&
+       res.code == 200
+      print_good("#{peer} - Logged out")
+    else
+      fail_with(Failure::NoAccess, "#{peer} - Attempted to logout, but failed")
+    end
   end
 
   def run_command(cmd, cookie)