hs-test: improved logging

- improved readability of some error messages
- printing container logs to stdout on test failure (last 20 lines)

Type: test

Change-Id: Idbb358bdd89aa7b1a6bdc9d96bf029d4c299ce64
Signed-off-by: adrianvillin <avillin@cisco.com>
diff --git a/extras/hs-test/linux_iperf_test.go b/extras/hs-test/linux_iperf_test.go
index c03403c..47ebd03 100644
--- a/extras/hs-test/linux_iperf_test.go
+++ b/extras/hs-test/linux_iperf_test.go
@@ -11,7 +11,7 @@
 
 	go s.startServerApp(srvCh, stopServerCh, nil)
 	err := <-srvCh
-	s.assertNil(err)
+	s.assertNil(err, err)
 	s.log("server running")
 
 	ipAddress := s.netInterfaces[tapInterfaceName].ip4AddressString()
@@ -19,6 +19,6 @@
 	s.log("client running")
 	s.log(<-clnRes)
 	err = <-clnCh
-	s.assertNil(err)
+	s.assertNil(err, "err: '%s', ip: '%s'", err, ipAddress)
 	s.log("Test completed")
 }