Fix the "search for sql.py" files for db models

Fix the search logic for sql.py files for the db model import so
that reflection created schemas are consistent.

This does not mitigate the need to move to stevedore in the future
for loading of backends / tests, but does solve the immidiate problem.

Change-Id: If53bfb351d679e3309393c7d594942c55daff3a6
Closes-Bug: #1310768
Merge "Fix the "search for sql.py" files for db models"