connect: use deterministic injected dynamic exposed port

This PR uses the checksum of the check for which a dynamic exposed
port is being generated (instead of a UUID prefix) so that the
generated port label is deterministic.

This fixes 2 bugs:
 - 'job plan' output is now idempotent for jobs making use of injected ports
 - tasks will no longer be destructively when jobs making use of injected ports
   are re-run without changing any user specified part of job config.

Fixes: #10099

nomad/job_endpoint_hook_expose_check.go

@@ -5,7 +5,6 @@ import (
 	"strconv"
 	"strings"
 
-	"github.com/hashicorp/nomad/helper/uuid"
 	"github.com/hashicorp/nomad/nomad/structs"
 	"github.com/pkg/errors"
 )
@@ -198,8 +197,9 @@ func exposePathForCheck(tg *structs.TaskGroup, s *structs.Service, check *struct
 	// This lets PortLabel be optional for any exposed check.
 	if check.PortLabel == "" {
 		port := structs.Port{
-			Label: fmt.Sprintf("svc_%s_ck_%s", s.Name, uuid.Generate()[:6]),
-			To:    -1,
+			HostNetwork: "default",
+			Label:       fmt.Sprintf("svc_%s_ck_%s", s.Name, check.Hash(s.Name)[:6]),
+			To:          -1,
 		}
 
 		tg.Networks[0].DynamicPorts = append(tg.Networks[0].DynamicPorts, port)

nomad/job_endpoint_hook_expose_check_test.go

@@ -343,6 +343,8 @@ func TestJobExposeCheckHook_exposePathForCheck(t *testing.T) {
 		ePath, err := exposePathForCheck(tg, s, c)
 		require.NoError(t, err)
 		require.Len(t, tg.Networks[0].DynamicPorts, 1)
+		require.Equal(t, "default", tg.Networks[0].DynamicPorts[0].HostNetwork)
+		require.Equal(t, "svc_", tg.Networks[0].DynamicPorts[0].Label[0:4])
 		require.Equal(t, &structs.ConsulExposePath{
 			Path:          "/health",
 			Protocol:      "",