test_s3: Add a test of multi-object delete.

Tests the implementation of the multi-object delete function call.

Signed-off-by: caleb miles <caleb.miles@inktank.com>
test_s3: Add a test of post object.

Tests the implementation of browser based uploads via a POST request
to publicly writable buckets.

Signed-off-by: caleb miles <caleb.miles@inktank.com>
test_s3: mark post test as fails_on_dho