Fix V3 API flavor returning empty string for attributes

Fixes cases where in the V3 API the ephemeral, swap and vcpus
attributes for flavors were returned as the empty string
when they had a value of 0. Also removes default setting for
the disabled attribute as it is always set in the db.

Fixes up some associated testcase data as it was using data which
could not exist in the db.

Change-Id: I90f48956411f792037b1cd744c4fa8d287f9e752
Closes-Bug: #1216929
Merge "Fix V3 API flavor returning empty string for attributes"