polish(sentinel): add mode for building lotus in sentinel mode

- replaces the sentinel flag on daemon command.

Makefile

@@ -331,3 +331,11 @@ docsgen:
 
 print-%:
 	@echo $*=$($*)
+
+# Sentinel build mode
+lotus-sentinel: $(BUILD_DEPS)
+	rm -f lotus
+	go build $(GOFLAGS) -ldflags="-X=github.com/filecoin-project/lotus/build.SentinelMode=true" -o lotus ./cmd/lotus
+	go run github.com/GeertJohan/go.rice/rice append --exec lotus -i ./build
+
+.PHONY: lotus

build/sentinel.go

@@ -0,0 +1,3 @@
+package build
+
+var SentinelMode string = "false"

cmd/lotus/daemon.go

@@ -13,6 +13,7 @@ import (
 	"net/http"
 	"os"
 	"runtime/pprof"
+	"strconv"
 	"strings"
 
 	paramfetch "github.com/filecoin-project/go-paramfetch"
@@ -128,10 +129,6 @@ var DaemonCmd = &cli.Command{
 			Usage:  "start lotus in lite mode",
 			Hidden: true,
 		},
-		&cli.BoolFlag{
-			Name:  "sentinel",
-			Usage: "start lotus in sentinel mode.",
-		},
 		&cli.StringFlag{
 			Name:  "pprof",
 			Usage: "specify name of file for writing cpu profile to",
@@ -517,7 +514,10 @@ func ImportChain(ctx context.Context, r repo.Repo, fname string, snapshot bool)
 
 func getDaemonMode(cctx *cli.Context) (daemonMode, error) {
 	isLite := cctx.Bool("lite")
-	isSentinel := cctx.Bool("sentinel")
+	isSentinel, err := strconv.ParseBool(build.SentinelMode)
+	if err != nil {
+		return modeUnknown, err
+	}
 
 	switch {
 	case !isLite && !isSentinel: