Refactor rspec test suite to remove duplications

Also, one of the tests was dependent of the privous, but even with-
out running the previous it would pass, but it wouldn't be testing
what it should. Now this test is not dependent on the previous one,
and its assertion will always happen after filtering by milestone:
The test in question is 'closes when the search bar is unfocused'

spec/features/issues/filtered_search/dropdown_milestone_spec.rb

@@ -39,9 +39,12 @@ describe 'Dropdown milestone', :js do
   end
 
   describe 'behavior' do
-    it 'opens when the search bar has milestone:' do
+    context 'filters by "milestone:"' do
+      before do
         filtered_search.set('milestone:')
+      end
 
+      it 'opens when the search bar has milestone:' do
         expect(page).to have_css(js_dropdown_milestone, visible: true)
       end
 
@@ -51,24 +54,21 @@ describe 'Dropdown milestone', :js do
         expect(page).to have_css(js_dropdown_milestone, visible: false)
       end
 
-    it 'shows loading indicator when opened' do
-      slow_requests do
-        filtered_search.set('milestone:')
-
-        expect(page).to have_css('#js-dropdown-milestone .filter-dropdown-loading', visible: true)
-      end
-    end
-
       it 'hides loading indicator when loaded' do
-      filtered_search.set('milestone:')
-
         expect(find(js_dropdown_milestone)).not_to have_css('.filter-dropdown-loading')
       end
 
       it 'loads all the milestones when opened' do
+        expect(filter_dropdown).to have_selector('.filter-dropdown .filter-dropdown-item', count: 6)
+      end
+    end
+
+    it 'shows loading indicator when opened' do
+      slow_requests do
         filtered_search.set('milestone:')
 
-      expect(filter_dropdown).to have_selector('.filter-dropdown .filter-dropdown-item', count: 6)
+        expect(page).to have_css('#js-dropdown-milestone .filter-dropdown-loading', visible: true)
+      end
     end
   end