Add concrete example for stack creation and update.

Replaces the placeholder-based example with a concrete one. The
example creates a simple stack and prints a hello world message.
Some parameter might be required to change for the example to
be reproducible (i.e. the flavor). The update operation switches
the flavor used in the earlier stack.

Change-Id: I10a7ab1afb3dd55be8865abe9c2b66d0d27ce948
Merge "Add concrete example for stack creation and update."