Require flavor on instance-create call in the CLI.

Instead of defaulting to flavor 1, the create-instance call will now
require that a flavorid is included with --flavor= on the command-line.

Implements blueprint no-default-flavor

Change-Id: I1de05bf4268d617b255e0be2fd2c999d49952c49
Merge "Require flavor on instance-create call in the CLI."