format: fix callAndRead for python3

See merge request nexedi/slapos.core!399

slapos/format.py

@@ -150,9 +150,12 @@ def getPublicIPv4Address():
       return ipv4
 
 def callAndRead(argument_list, raise_on_error=True):
-  popen = subprocess.Popen(argument_list,
-                           stdout=subprocess.PIPE,
-                           stderr=subprocess.STDOUT)
+  popen = subprocess.Popen(
+    argument_list,
+    stdout=subprocess.PIPE,
+    stderr=subprocess.STDOUT,
+    universal_newlines=True,
+  )
   result = popen.communicate()[0]
   if raise_on_error and popen.returncode != 0:
     raise ValueError('Issue while invoking %r, result was:\n%s' % (

slapos/tests/test_slapformat.py

@@ -950,5 +950,9 @@ class TestFormatConfig(SlapformatMixin):
 
   # TODO add more tests with config file
 
-if __name__ == '__main__':
-  unittest.main()
+
+class TestCallAndRead(unittest.TestCase):
+  def test_callAndRead(self):
+    self.assertEqual(
+      slapos.format.callAndRead(['echo', 'hello']),
+      (0, 'hello\n'))