Bug: change default cluster create experience to require --id cli parameter (#112)

* change default cluster create experience to require --id cli parameter

* updated error message to reflect intended workflow

config/cluster.yaml

@@ -1,7 +1,6 @@
 ##  cluster settings
 
-# id: <id of the cluster to be created>
-id: spark_cluster
+# id: <id of the cluster to be created, reccommended to specify with --id command line parameter>
 
 # vm_size: <vm-size, see available options here: https://azure.microsoft.com/en-us/pricing/details/virtual-machines/linux/>
 vm_size: standard_a2

dtde/config.py

@@ -174,7 +174,7 @@ class ClusterConfig:
 
         if self.uid is None:
             raise error.ThunderboltError(
-                    "Please supply an id for the cluster either in the cluster.yaml configuration file or with a parameter (--id)")
+                    "Please supply an id for the cluster with a parameter (--id)")
 
         if self.size == 0 and self.size_low_pri == 0:
             raise error.ThunderboltError(