Add waiting for submit button in tables tests

tests/integration/test_table.py

@@ -50,6 +50,7 @@ class MentoringTableBlockTest(MentoringBaseTest):
         answers[1].send_keys('This is the answer #2')
         submit = mentoring.find_element_by_css_selector('.submit input.input-main')
         submit.click()
+        self.wait_until_disabled(submit)
 
         table = self.go_to_page('Table 2', css_selector='.mentoring-table')
         rows = table.find_elements_by_css_selector('td')