Improve command-line client error output (#122)

Motivation: The output when an error occurs shows an integer error code,
which isn't very helpful. And in the case of an error when creating a
resource, you also get a redundant log message from the controller
client.

Modifications:
* the controller client no longer logs errors
* the generated String() allows for the enum name to be displayed in the
  error output
* each errorCode enum member has a hand-generated description
* the format of the error message from the CLI client was modified to
  display the error description with the error message

Related to #112

types.go

@@ -72,6 +72,7 @@ type (
 		Code    errorCode `json:"code"`
 		Message string    `json:"message"`
 	}
+
 	errorCode int
 )
 
@@ -85,3 +86,14 @@ const (
 	ErrorNoSpace
 	ErrorNotImplmented
 )
+
+// must match order and len of the above const
+var errorDescriptions = []string{
+	"Internal error",
+	"Not authorized",
+	"Resource not found",
+	"Resource exists",
+	"Invalid argument",
+	"No space",
+	"Not implemented",
+}