backfill region from job hcl in jobUpdate and jobPlan endpoints

- updated region in job metadata that gets persisted to nomad datastore
- fixed many unrelated unit tests that used an invalid region value
(they previously passed because hcl wasn't getting picked up and
the job would default to global region)

command/agent/testingutils_test.go

@@ -109,3 +109,9 @@ func MockPeriodicJob() *api.Job {
 	}
 	return j
 }
+
+func MockRegionalJob() *api.Job {
+	j := MockJob()
+	j.Region = helper.StringToPtr("north-america")
+	return j
+}