seleniumserver/test: fix flaky test

This test was just checking the data from the first recv call, but the
data might arrive in multiple times. Call recv in a loop until we
received the end of the expected message (or until timeout when
something goes wrong).

software/seleniumserver/test/test.py

@@ -381,11 +381,15 @@ class TestSSHServer(SeleniumServerTestCase):
 
       channel = client.invoke_shell()
       channel.settimeout(30)
-      # apparently we sometimes need to send something on the first ssh connection
-      channel.send('\n')
-      # openssh prints a warning 'Attempt to write login records by non-root user (aborting)'
-      # so we received more than the lenght of the asserted message.
-      self.assertIn("Welcome to SlapOS Selenium Server.", channel.recv(100))
+      received = ''
+      while True:
+        r = channel.recv(1024)
+        if not r:
+          break
+        received += r
+        if 'Selenium Server.' in received:
+          break
+      self.assertIn("Welcome to SlapOS Selenium Server.", received)
 
 
 class TestFirefox52(BrowserCompatibilityMixin, SeleniumServerTestCase):