Align status output for parallel_execute

Previously docker-compose would output lines that looked like:

    Starting service ... done
    Starting short ...
    Starting service-with-a-long-name ... done

It's difficult to scan down this output and get an idea of what's happening.

Now the statuses are aligned, and output looks like this:

    Starting service                  ... done
    Starting short                    ...
    Starting service-with-a-long-name ... done

To me, this is quite a bit easier to read.

Signed-off-by: Evan Shaw <evan@vendhq.com>

tests/unit/parallel_test.py

@@ -115,3 +115,18 @@ def test_parallel_execute_with_upstream_errors():
     assert (data_volume, None, APIError) in events
     assert (db, None, UpstreamError) in events
     assert (web, None, UpstreamError) in events
+
+
+def test_parallel_execute_alignment(capsys):
+    results, errors = parallel_execute(
+        objects=["short", "a very long name"],
+        func=lambda x: x,
+        get_name=six.text_type,
+        msg="Aligning",
+    )
+
+    assert errors == {}
+
+    _, err = capsys.readouterr()
+    a, b = err.split('\n')[:2]
+    assert a.index('...') == b.index('...')