Filter available flavors for each service

Filter the flavors that show up in the dropdown when deploying
an application using a new "requirements" config imported thru
a package's yaml file.

Change-Id: I77d1f560c42d7ea25b9ecd7b4cadc8e7c2ae43ff
Implements: blueprint filter-flavor-for-each-service
Merge "Filter available flavors for each service"