Try to fix test_mpi_roundtrip tests not finising. Use Popen.communicate as it…

theano/tensor/tests/_test_mpi_roundtrip.py

@@ -42,6 +42,7 @@ if rank == 0:
     _, zz = f(xx)
 
     same = np.linalg.norm(zz - expected) < .001
+    # The parent test will look for "True" in the output
     stdout.write(str(same))
 
 if rank == 1:

theano/tensor/tests/test_mpi.py

@@ -52,8 +52,10 @@ def test_mpi_roundtrip():
                          stderr=subprocess.PIPE,
                          shell=True,
                          close_fds=True)
-    result = theano.compat.decode(p.stdout.read())
-    assert "True" in result, theano.compat.decode(p.stderr.read())
+    (stdout, stderr) = p.communicate()
+
+    result = theano.compat.decode(stdout)
+    assert "True" in result, theano.compat.decode(stderr)
 
 
 def test_mpi_send_wait_cmp():