BUG: Fix end session metadata for minute bar writer.

When opening with a new `end_session`, i.e. opening for append, write the new
end session to the metadata.

Fixes an issue where the calendar on minute bar readers did not include the
recently appended day, causing reads on the last values to fail.

According, update append test to read a value, instead of checking table length.

tests/data/test_minute_bars.py

@@ -439,40 +439,42 @@ class BcolzMinuteBarTestCase(WithTradingCalendars,
             'volume': [10.0]
         }
 
-        first_minute = self.market_opens[TEST_CALENDAR_START]
+        dt = self.market_opens[TEST_CALENDAR_STOP]
         data = DataFrame(
             data=ohlcv,
-            index=[first_minute])
+            index=[dt])
         self.writer.write_sid(sid, data)
 
         # Open a new writer to cover `open` method, also a common usage
         # of appending new days will be writing to an existing directory.
         cday = self.trading_calendar.schedule.index.freq
-        new_end_session = TEST_CALENDAR_START + cday
+        new_end_session = TEST_CALENDAR_STOP + cday
         writer = BcolzMinuteBarWriter.open(self.dest, new_end_session)
-        next_day_minute = first_minute + cday
+        next_day_minute = dt + cday
         new_data = DataFrame(
             data=ohlcv,
             index=[next_day_minute])
         writer.write_sid(sid, new_data)
 
-        second_minute = first_minute + Timedelta(minutes=1)
+        # Get a new reader to test updated calendar.
+        reader = BcolzMinuteBarReader(self.dest)
+
+        second_minute = dt + Timedelta(minutes=1)
 
         # The second minute should have been padded with zeros
         for col in ('open', 'high', 'low', 'close'):
             assert_almost_equal(
-                nan, self.reader.get_value(sid, second_minute, col)
+                nan, reader.get_value(sid, second_minute, col)
             )
         self.assertEqual(
-            0, self.reader.get_value(sid, second_minute, 'volume')
+            0, reader.get_value(sid, second_minute, 'volume')
         )
 
-        # The first day should contain US_EQUITIES_MINUTES_PER_DAY rows.
-        # The second day should contain a single row.
-        self.assertEqual(
-            len(self.writer._ensure_ctable(sid)),
-            US_EQUITIES_MINUTES_PER_DAY + 1,
-        )
+        # The next day minute should have data.
+        for col in ('open', 'high', 'low', 'close', 'volume'):
+            assert_almost_equal(
+                ohlcv[col], reader.get_value(sid, next_day_minute, col)
+            )
 
     def test_write_multiple_sids(self):
         """

zipline/data/minute_bars.py

@@ -497,7 +497,7 @@ class BcolzMinuteBarWriter(object):
             metadata.minutes_per_day,
             metadata.default_ohlc_ratio,
             metadata.ohlc_ratios_per_sid,
-            write_metadata=False
+            write_metadata=end_session is not None
         )
 
     @property