setup.py: Add "package" directory to the package list (#50)

ImportLib was unable to find the package module when Rift was installed
with setupy.py because it was no declared in the package list and thus,
not included in the resulting egg archive.

Author: qa-cea

setup.py

@@ -41,7 +41,7 @@
       author='Aurelien Cedeyn',
       author_email='aurelien.cedeyn@cea.fr',
       package_dir={'': 'lib'},
-      packages=['rift'],
+      packages=['rift', 'rift.package'],
       install_requires=['boto3>=1.18.65', 'xmltodict'],
       py_modules = ['unidiff'],
       data_files = [