Add instance-actions,flavors,flavor-rxtx metafiles for api-samples

Converts instance-actions,flavors,flavor-rxtx api sample to create
meta files for api sample docs.
We use this to auto generate the specification document.

And add 'extension_name' for flavors api samples to ensure generating
'extenion' attribute in metafiles.

Change-Id: Icace5d17666cdbf29310119bc96d20335092b87e