Fix flake8 errors and warnings

We add the flake8 configuration used so we ensure everyone uses the same.
We remove the usage of __all__ for non public API.
When possible, we rationalize the class name according to its __name__ and module.

issue9082
review297061002

.flake8

@@ -0,0 +1,2 @@
+[flake8]
+ignore=E123,E124,E126,E128,W503

carrier.py

@@ -6,8 +6,6 @@ from trytond.transaction import Transaction
 from trytond.pool import Pool, PoolMeta
 from trytond.pyson import Eval
 
-__all__ = ['Carrier']
-
 
 class Carrier(metaclass=PoolMeta):
     __name__ = 'carrier'

sale.py

@@ -4,8 +4,6 @@ from decimal import Decimal
 
 from trytond.pool import PoolMeta
 
-__all__ = ['Sale']
-
 
 class Sale(metaclass=PoolMeta):
     __name__ = 'sale.sale'

setup.py

@@ -81,8 +81,9 @@ setup(name=name,
     keywords='tryton carrier percentage',
     package_dir={'trytond.modules.carrier_percentage': '.'},
     packages=(
-        ['trytond.modules.carrier_percentage'] +
-        ['trytond.modules.carrier_percentage.%s' % p for p in find_packages()]
+        ['trytond.modules.carrier_percentage']
+        + ['trytond.modules.carrier_percentage.%s' % p
+            for p in find_packages()]
         ),
     package_data={
         'trytond.modules.carrier_percentage': (info.get('xml', [])
@@ -96,7 +97,8 @@ setup(name=name,
         'Intended Audience :: Financial and Insurance Industry',
         'Intended Audience :: Legal Industry',
         'Intended Audience :: Manufacturing',
-        'License :: OSI Approved :: GNU General Public License v3 or later (GPLv3+)',
+        'License :: OSI Approved :: '
+        'GNU General Public License v3 or later (GPLv3+)',
         'Natural Language :: Bulgarian',
         'Natural Language :: Catalan',
         'Natural Language :: Chinese (Simplified)',

stock.py

@@ -5,8 +5,6 @@ from decimal import Decimal
 from trytond.pool import Pool, PoolMeta
 from trytond.transaction import Transaction
 
-__all__ = ['ShipmentIn', 'ShipmentOut']
-
 
 def _percentage_amount(lines, company):
     pool = Pool()

tests/__init__.py

@@ -2,7 +2,7 @@
 # this repository contains the full copyright notices and license terms.
 
 try:
-    from trytond.modules.carrier_percentage.tests.test_carrier_percentage import suite
+    from trytond.modules.carrier_percentage.tests.test_carrier_percentage import suite  # noqa: E501
 except ImportError:
     from .test_carrier_percentage import suite