Port horizon tabs tests to Python 3

* get_cells(): cast dict.values() to a list to return a list
  on Python 3. On Python 3, dict.values() now returns a view.
* Replace dict.values()[0] with list(dict.values())[0]
* get_tabs(): replace filter() with a list-comprehension to return a
  list on Python 3
* tox.ini: add horizon.test.tests.tabs to Python 3.4

Partial-Implements: blueprint porting-python3
Change-Id: I0ebcaa5f7b283d04425ce7201087220376257d41

horizon/tables/base.py

@@ -442,7 +442,7 @@ class Column(html.HTMLElement):
 
         summation_function = self.summation_methods[self.summation]
         data = [self.get_raw_data(datum) for datum in self.table.data]
-        data = filter(lambda datum: datum is not None, data)
+        data = [raw_data for raw_data in data if raw_data is not None]
 
         if len(data):
             try:
@@ -605,7 +605,7 @@ class Row(html.HTMLElement):
 
     def get_cells(self):
         """Returns the bound cells for this row in order."""
-        return self.cells.values()
+        return list(self.cells.values())
 
     def get_ajax_update_url(self):
         table_url = self.table.get_absolute_url()
@@ -1396,7 +1396,7 @@ class DataTable(object):
         """hide checkbox column if no current table action is allowed."""
         if not self.multi_select:
             return
-        select_column = self.columns.values()[0]
+        select_column = list(self.columns.values())[0]
         # Try to find if the hidden class need to be
         # removed or added based on visible flag.
         hidden_found = 'hidden' in select_column.classes

horizon/tabs/base.py

@@ -177,7 +177,7 @@ class TabGroup(html.HTMLElement):
 
     def get_tabs(self):
         """Returns a list of the allowed tabs for this tab group."""
-        return filter(lambda tab: tab._allowed, self._tabs.values())
+        return [tab for tab in self._tabs.values() if tab._allowed]
 
     def get_tab(self, tab_name, allow_disabled=False):
         """Returns a specific tab from this tab group.

tox.ini

@@ -27,6 +27,7 @@ commands =
         horizon.test.tests.messages \
         horizon.test.tests.middleware \
         horizon.test.tests.tables.DataTableViewTests \
+        horizon.test.tests.tabs \
         horizon.test.tests.templatetags \
         horizon.test.tests.test_file_discovery \
         horizon.test.tests.utils.FiltersTests \