Cleanup container update headers in obj server tests

The object server tests for container backed headers were doing a match
expectation against the backend HeaderKeyDict using a real dict so in tests
the keys were needlessly case sensitive.  This change updates the tests so
they perform correct assertions with case insensitive header keys and removes
some needless string manipulation in the obj server added to satisfy the
overly picky unittests.

There's also a drive by fix to update some backend http mocks for container
update tests that we're not fully exercising their their request fakes.
Because the object server container update code is resilient to to all manor
of failure from backend requests the general intent of the tests was
unaffected but this change cleans up some confusing logging in the debug
logger output.

Change-Id: Iea5ed128b62fd2dc17f55cd8076b711e6087dd26
Merge "Cleanup container update headers in obj server tests" into feature/ec