Port 'RecordsetCrossZoneTest' to plugin

These tests were for the /v2/recordsets endpoint, so I've augmented
the tests that currently exist.

Ported:
`test_get_single_recordset` -> `test_get_single_zones_recordsets`
`test_list_recordsets` -> `test_list_zones_recordsets_zone_names`
`test_filter_recordsets` augmented `test_list_filter_zones_recordsets`

Change-Id: Ie79f201bc7b92328b77ce05fd0b0eebc63330c9f
2 files changed