Fix random bug when workstation_name is < 6 chars

When the local workstation name is less than 6 characters, remote
authentication against a Windows 2008r2 WinRM service always fails. This
doesn't seem to affect authentication against IIS's negotiate
implementation.

Author: egypt

lib/rex/proto/http/client.rb

@@ -480,7 +480,7 @@ def negotiate_auth(opts={})
     opts['headers']||= {}
 
     ntlmssp_flags = ::Rex::Proto::NTLM::Utils.make_ntlm_flags(ntlm_options)
-    workstation_name = Rex::Text.rand_text_alpha(rand(8)+1)
+    workstation_name = Rex::Text.rand_text_alpha(rand(8)+6)
     domain_name = self.config['domain']
 
     b64_blob = Rex::Text::encode_base64(