Added DorFetcher Client instance variable

No longer calling druids_via_oai so updating tests to reflect the new call to dor_fetcher_client.druid_array
Generated and added VCR cassette yml files so our tests don't rely on a network connection
In order to remove repetitive data in the collection yml files, added yml config file for dor-fetcher-service URL and cleaned up example files and logging messages

@bess @carrickr