SITE: Update test recording instructions

This is required to better describe recent changes
for parameterizing recording and provider configuration
of credentials and resources to avoid having to edit
test source code in order to record test fixtures.
TrackedAt: http://tracker.deltacloud.org/patch/9723a4aa34c7b445973301facebb13399064aab4
tests/drivers: set rerecord mode base on env. var. VCR_RECORD

This patch updates the driver white box tests to trigger re-recording
based on the environment variable VCR_RECORD.
TrackedAt: http://tracker.deltacloud.org/patch/ddfec85749e851f1d772cf5dc4e433bc64f77888