tests/functional: move uncompress handling into new uncompress.py file

tests/functional: move uncompress handling into new uncompress.py file

More uncompress related code will be added shortly, so having a
separate file makes more sense.

The utils.py imports the functions from archive.py, so that
existing callers don't need to be modified. This avoids
redundant code churn until later in the series when all
calls will be adapted for other reasons.

Reviewed-by: Thomas Huth <thuth@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20241217155953.3950506-18-berrange@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>