Handle bracketed and unbracketed results, add more useful logging

modules/exploits/multi/elasticsearch/script_mvel_rce.rb

@@ -120,7 +120,13 @@ class Metasploit3 < Msf::Exploit::Remote
   end
 
   def parse_result(res)
-    unless res && res.code == 200 && res.body
+    unless res
+      vprint_error("#{peer} no response")
+      return nil
+    end
+
+    unless res.code == 200 && res.body
+      vprint_error("#{peer} responded with HTTP code #{res.code} (with#{res.body ? '' : 'out'} a body)")
       return nil
     end
 
@@ -136,7 +142,7 @@ class Metasploit3 < Msf::Exploit::Remote
       return nil
     end
 
-    result
+    result.is_a?(::Array) ? result.first : result
   end
 
   def java_sum(summands)