Added db support to filter out the vnf packages as per the
filter rule specified in the `filter` query parameter.
Made use of ready-made 'sqlalchemy-filters' library which
can apply filters to the query object dynamically.
You can find few examples on home page of sqlalchemy-filters
github repository:
https://github.com/juliotrigo/sqlalchemy-filters
Change-Id: Iddf0ba7445fa7739440d333d914e675bd0782040
Implements: bp/enhance-vnf-package-support-part1