Fixes inconsistency in flavors list with marker

Flavors list with marker is supposed to use flavorid as the marker since this is
the only id attribute the users can see, but it was using id (the confusion was
probably caused by the fact that flavorid attribute shows up to the user as id).

The change on db unit test shows makes the bug evident, and justify the changes
on the filter_by criteria.

Fixes bug 1226698

Change-Id: I3ffa636febb63be796fffc94be6486bf74e8239b
Merge "Fixes inconsistency in flavors list with marker"