hs-test: fix logs once again

- "/dev/null" and "tail: ..." messages should now be
  removed properly

Type: test

Change-Id: I4aa1f1a1cab17dab73f727e40c80a44d6e753bd5
Signed-off-by: Adrian Villin <avillin@cisco.com>

extras/hs-test/infra/container.go

@@ -468,12 +468,12 @@ func (c *Container) log(maxLines int) (string, error) {
 	stdout := stdoutBuf.String()
 	stderr := stderrBuf.String()
 
-	if strings.Contains(stdout, "==> /dev/null <==") {
-		stdout = ""
-	}
-	if strings.Contains(stderr, "tail: cannot open") {
-		stderr = ""
-	}
+	stdout = strings.Join(strings.Split(stdout, "==> /dev/null <=="), "")
+	stderr = strings.Join(strings.Split(stderr, "tail: cannot open '' for reading: No such file or directory"), "")
+
+	// remove empty lines after deleting the above-mentioned messages
+	stdout = strings.TrimSpace(stdout)
+	stderr = strings.TrimSpace(stderr)
 
 	return stdout + stderr, err
 }