add profiler support

profiling is now available via the HTTP base URL /debug/pprof/

examples, use this URL to start and download a 30 seconds CPU profile:

/debug/pprof/profile?seconds=30

use this URL to profile used memory:

/debug/pprof/heap?gc=1

use this URL to profile allocated memory:

/debug/pprof/allocs?gc=1

Full docs here:

https://golang.org/pkg/net/http/pprof/

sftpd/sftpd_test.go

@@ -197,7 +197,7 @@ func TestMain(m *testing.M) {
 	}()
 
 	go func() {
-		if err := httpdConf.Initialize(configDir); err != nil {
+		if err := httpdConf.Initialize(configDir, false); err != nil {
 			logger.Error(logSender, "", "could not start HTTP server: %v", err)
 		}
 	}()