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

error.go

@@ -23,8 +23,8 @@ import (
 	"strings"
 )
 
-func (e Error) Error() string {
-	return fmt.Sprintf("(Error %v) %v", e.Code, e.Message)
+func (err Error) Error() string {
+	return fmt.Sprintf("%v - %v", err.Description(), err.Message)
 }
 
 func MakeError(code int, msg string) Error {
@@ -90,3 +90,11 @@ func GetHTTPError(err error) (int, string) {
 	}
 	return code, msg
 }
+
+func (err Error) Description() string {
+	idx := int(err.Code)
+	if idx < 0 || idx > len(errorDescriptions)-1 {
+		return ""
+	}
+	return errorDescriptions[idx]
+}