backport Quantum metadata support

fixes: DHC-476

Backports the Nova Grizzly Metadata services changes that support
overlapping networks.  This can be used by updating Nova api-paste.ini
file to:

[app:metaapp]
paste.app_factory = \
akanda.nova.folsom.metadata.handler:MetadataRequestHandler.factory
Merge pull request #61 from markmcclain/meta

backport Quantum metadata support