[PATCH] testsuite: Improve SSH ping

[Uladzimir Bely <ubely@ilbers.de>]

When qemu machine boots, it may happen that consecutive SSH connection
fails right after the previous good one. So, we get a situation when
the command/script fails after we consider SSH is ready.

This patch improves detection of SSH server ready status by making at
least three good consecutive SSH pings.

Example of debug output that shows the case:

```
| Waiting for SSH server ready...
| SSH ping result: 255, left: 300s # <== machine is booting
| SSH ping result: 255, left: 294s
| SSH ping result: 255, left: 288s
| SSH ping result: 255, left: 282s
| SSH ping result: 255, left: 276s
| SSH ping result: 255, left: 270s
| SSH ping result: 255, left: 264s
| SSH ping result: 255, left: 258s
| SSH ping result: 0, left: 253s   # <== SSH server is up...
| SSH ping result: 0, left: 251s
| SSH ping result: 255, left: 250s # <== but one ping failed again
| SSH ping result: 0, left: 248s
| SSH ping result: 0, left: 245s
| SSH ping result: 0, left: 243s
| SSH server is ready
| `lsmod | grep example_module` returned 0
```

Signed-off-by: Uladzimir Bely <ubely@ilbers.de>
---
 testsuite/cibuilder.py | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/testsuite/cibuilder.py b/testsuite/cibuilder.py
index 9e84c3a3..4e568b8e 100755
--- a/testsuite/cibuilder.py
+++ b/testsuite/cibuilder.py
@@ -257,17 +257,25 @@ class CIBuilder(Test):
         self.log.debug('Waiting for SSH server ready...')
 
         rc = None
+        goodcnt = 0
         while time.time() < timeout:
             if proc.poll() is not None:
                 self.log.error('Machine is not running')
                 return rc
 
             rc = self.exec_cmd('/bin/true', cmd_prefix)
+            time_left = timeout - time.time()
+            self.log.debug('SSH ping result: %d, left: %.fs' % (rc, time_left))
             time.sleep(1)
 
             if rc == 0:
-                self.log.debug('SSH server is ready')
-                break
+                goodcnt += 1
+                # Let 3 good SSH pings to make sure SSH connection is stable
+                if goodcnt >= 3:
+                    self.log.debug('SSH server is ready')
+                    break
+            else:
+                goodcnt = 0
 
         if rc != 0:
             self.log.error('SSH server is not ready')
-- 
2.20.1