Switch from fluentd to fluentbit for log forwarding (#1086)

This removes fluentd in favor of using fluentbit, which is lighter (in
memory usage) and seems to be more actively maintained.

Fluentbit's config file format is different from fluentd's.  It also
doesn't support the same record modification stuff that fluentd
supports, so we have to change the influxdb query slightly.  This
means that after an upgrade, the new CLI may won't work for querying older 
logs.  Hopefully, this slight breakage is acceptable; if users 
really need older logs they can use the older CLI.

executor/executor.go

@@ -20,7 +20,6 @@ import (
 	"context"
 	"fmt"
 	"net/http"
-	"runtime/debug"
 	"strings"
 	"sync"
 	"time"
@@ -193,10 +192,6 @@ func (executor *Executor) isValidAddress(fsvc *fscache.FuncSvc) bool {
 	}
 }
 
-func dumpStackTrace() {
-	debug.PrintStack()
-}
-
 func serveMetric(logger *zap.Logger) {
 	// Expose the registered metrics via HTTP.
 	metricAddr := ":8080"