console: use templates to build SQL query

This is needed if we want to be able to mix use of several tables
inside a single query (for example, flows_1m0s for a part of the query
and flows_5m0s for another part to overlay historical data).

Also, the way we handle time buckets is now cleaner. The previous way
had two stages of rounding and was incorrect. We were discarding the
first and last value for this reason. The new way only has one stage
of rounding and is correct. It tries hard to align the buckets at the
specified start time. We don't need to discard these values anymore.
We still discard the last one because it could be incomplete (when end
is "now").

console/widgets_test.go

@@ -6,6 +6,7 @@ package console
 import (
 	"net"
 	"reflect"
+	"strings"
 	"testing"
 	"time"
 
@@ -229,18 +230,18 @@ func TestWidgetGraph(t *testing.T) {
 		{base.Add(5 * time.Minute), 24.7},
 	}
 	mockConn.EXPECT().
-		Select(gomock.Any(), gomock.Any(), `
+		Select(gomock.Any(), gomock.Any(), strings.TrimSpace(`
 SELECT
- toStartOfInterval(TimeReceived, INTERVAL 864 second) AS Time,
+ toStartOfInterval(TimeReceived + INTERVAL 144 second, INTERVAL 864 second) - INTERVAL 144 second AS Time,
  SUM(Bytes*SamplingRate*8/864)/1000/1000/1000 AS Gbps
 FROM flows
 WHERE TimeReceived BETWEEN toDateTime('2009-11-10 23:00:00', 'UTC') AND toDateTime('2009-11-11 23:00:00', 'UTC')
 AND InIfBoundary = 'external'
 GROUP BY Time
 ORDER BY Time WITH FILL
- FROM toStartOfInterval(toDateTime('2009-11-10 23:00:00', 'UTC'), INTERVAL 864 second)
+ FROM toDateTime('2009-11-10 23:00:00', 'UTC')
  TO toDateTime('2009-11-11 23:00:00', 'UTC')
- STEP 864`).
+ STEP 864`)).
 		SetArg(1, expected).
 		Return(nil)