Update the artifacts stored in stage2

This change updates the patterns of the artifacts to be stored by the
method `archive` in `ci_helper.groovy`.

The pattern "dists/*.gz" and "dists/*Packages" corresponding to index
files for debian repos are no longer required.

The pattern "dist/*.whl" corresponding to Python wheel files is now
required, since it is an additional artifact generated in stage2.

Change-Id: Id87fcb98b2d79a9bd0b64fdaca44da8acd9e1cb1
Signed-off-by: garciadeblas <gerardo.garciadeblas@telefonica.com>