oversubscription: add memory_max to hclv1

Allow specifying the `memory_max` field in HCL under the resources block.

Though HCLv1 is deprecated, I've updated them to ease our testing.

jobspec/parse_task.go

@@ -548,6 +548,7 @@ func parseResources(result *api.Resources, list *ast.ObjectList) error {
 		"iops", // COMPAT(0.10): Remove after one release to allow it to be removed from jobspecs
 		"disk",
 		"memory",
+		"memory_max",
 		"network",
 		"device",
 	}

jobspec/parse_test.go

@@ -285,8 +285,9 @@ func TestParse(t *testing.T) {
 									"LOREM": "ipsum",
 								},
 								Resources: &api.Resources{
-									CPU:      intToPtr(500),
-									MemoryMB: intToPtr(128),
+									CPU:         intToPtr(500),
+									MemoryMB:    intToPtr(128),
+									MemoryMaxMB: intToPtr(256),
 									Networks: []*api.NetworkResource{
 										{
 											MBits:         intToPtr(100),

jobspec/test-fixtures/basic.hcl

@@ -227,8 +227,9 @@ job "binstore-storagelocker" {
       }
 
       resources {
-        cpu    = 500
-        memory = 128
+        cpu        = 500
+        memory     = 128
+        memory_max = 256
 
         network {
           mbits = "100"