MAINT: Fix failures/warnings in test_api_shim.py

- Fixes a warning on indexing with a float that ultimately came from
  pd.Timedelta.total_seconds().  Adds ``timedelta_to_integral_seconds``
  and ``timedelta_to_integral_minutes()`` functions and replaces various
  usages of ``int(delta.total_seconds())`` with them.

- Fixes a warnings triggered in ``_create_daily_stats`` from
  passing tz-aware datetimes to np.datetime64.

zipline/algorithm.py

@@ -819,8 +819,9 @@ class TradingAlgorithm(object):
             else:
                 self.risk_report = perf
 
-        daily_dts = [np.datetime64(perf['period_close'], utc=True)
-                     for perf in daily_perfs]
+        daily_dts = pd.DatetimeIndex(
+            [p['period_close'] for p in daily_perfs], tz='UTC'
+        )
         daily_stats = pd.DataFrame(daily_perfs, index=daily_dts)
 
         return daily_stats