Test top-to-bottom: object-store containers

Replicate the object-store container command tests but use requests_mock
to test the entire stack down to the requests module.

Thess will be useful regressions tests when the existing object-store lib
modules are moved to the low-level API object.

Change-Id: Ibf25be46156eb1009f1b66f02f2073d3913b846d
Merge branch 'obj-test-end-to-end' into dt-test
Merge branch 'low-level-api-base' into dt-test
Merge branch 'low-level-api-object' into dt-test
Merge branch 'identity-ec2-tests' into dt-test