Remove useless api sample template files for flavor-rxtx v3

flavor-rxtx template files flavor-get-resp.* and flavors-detail-resp.*
isn't used by any api sample test. So remove them.

Change-Id: I74760bcd5367487aca31cdf94fa5e5715f19f4c6
Add decorator expected_errors for flavors_extraspecs v3

This patch add decorator expected_errors and also add catching
for FlavorNotFound.

Partially implements bp nova-v3-api

DocImpact

Change-Id: I56556871f649ba56211d3f523a184e3171dd3b7e
Merge "Add decorator expected_errors for flavors_extraspecs v3"
Merge "Remove useless api sample template files for flavor-rxtx v3"