Tests: unitd stderr output redirected to unit.log.

A part of the debug log was printed to stderr before the log file was opened.
Now, this output is redirected to the same log file.

test/unit/main.py

@@ -209,8 +209,7 @@ class TestUnit(unittest.TestCase):
 
         os.mkdir(self.testdir + '/state')
 
-        print()
-
+        with open(self.testdir + '/unit.log', 'w') as log:
             self._p = subprocess.Popen(
                 [
                     self.unitd,
@@ -220,7 +219,8 @@ class TestUnit(unittest.TestCase):
                     '--pid',      self.testdir + '/unit.pid',
                     '--log',      self.testdir + '/unit.log',
                     '--control',  'unix:' + self.testdir + '/control.unit.sock',
-            ]
+                ],
+                stderr=log,
             )
 
         if not self.waitforfiles(self.testdir + '/control.unit.sock'):