Incorporate integration testing

[wagoodman]

Introduce integration-level testing that tests:

• imgbom to vulnscan integrations: the appropriate package catalog is obtained from an underlying image
• vulnscan to vulnscan-db: the appropriate store can be obtained from a flat file
• internal vulnscan matching: given a catalog and vulnerability db obtained from standard execution paths, verify select matching results (direct exact matches, indirect matches, cpe matching, various vulnerability input sources appear in the results, etc)

[wagoodman]

blocking since we're splitting the vulnscan repo & https://github.com/anchore/vulnscan-db/issues/30 will change the interface format substantially enough to probably wait for these changes to drop first.