Remove code duplication from s3 tests.

A new module, s3_utilities.pm has been created.  It contains
subroutines common to at least two of the workunits in this
directory. Code was moved here from the other pl files, and
some minor changes (paramers and scope changes) were needed.

Fixes: 7472
Signed-off-by: Warren Usui <warren.usui@inktank.com>
Merge pull request #1465 from ceph/wip-s3pm-wusui

Remove code duplication from s3 tests.