Block networking in sandbox test by default, fix roughtime panic (#3240)

* block networking in sandbox test by default, fix roughtime panic

* Update .bazelrc

shared/roughtime/BUILD.bazel

@@ -7,6 +7,7 @@ go_library(
     visibility = ["//visibility:public"],
     deps = [
         "@com_github_cloudflare_roughtime//:go_default_library",
+        "@com_github_sirupsen_logrus//:go_default_library",
         "@com_googlesource_roughtime_roughtime_git//go/config:go_default_library",
     ],
 )

shared/roughtime/roughtime.go

@@ -6,6 +6,7 @@ import (
 	"time"
 
 	rt "github.com/cloudflare/roughtime"
+	"github.com/sirupsen/logrus"
 	"roughtime.googlesource.com/roughtime.git/go/config"
 )
 
@@ -22,6 +23,8 @@ func mustDecodeString(in string) []byte {
 	return pk
 }
 
+var log = logrus.WithField("prefix", "roughtime")
+
 func init() {
 	t0 := time.Now()
 
@@ -71,7 +74,7 @@ func init() {
 	var err error
 	offset, err = rt.AvgDeltaWithRadiusThresh(results, t0, 2*time.Second)
 	if err != nil {
-		panic(err)
+		log.WithError(err).Error("Failed to calculate roughtime offset")
 	}
 }