fix to handle object-expiration headers in one method

There was some duplication of code in both POST and PUT
methods to handle object-expiration headers.
A method was created to remove this duplication,
which should help with maintainability of code.

Change-Id: I85cc4a7b0d688760c97598d80b9e9a39288c5f34
Signed-off-by: Thiago da Silva <thiago@redhat.com>