Fix issue with user command and user email already exist

backend/tracim_backend/command/user.py

                     "You must provide -p/--password parameter"
                 )
             password = ''
-
+        if self._user_api.check_email_already_in_db(login):
+            raise UserAlreadyExistError()
         try:
             user = self._user_api.create_user(
                 email=login,
             # daemons = DaemonsManager()
             # daemons.run('radicale', RadicaleDaemon)
             self._user_api.execute_created_user_actions(user)
-        except IntegrityError:
+        except IntegrityError as exception:
             self._session.rollback()
-            raise UserAlreadyExistError()
+            raise UserAlreadyExistError() from exception
         except NotificationNotSend as exception:
             self._session.rollback()
-            raise exception
+            raise exception from exception
 
         return user
 

backend/tracim_backend/lib/core/user.py

         if not is_email_correct:
             raise EmailValidationFailed(
                 'Email given form {} is uncorrect'.format(email))  # nopep8
-        email_already_exist_in_db = self._check_email_already_in_db(email)
+        email_already_exist_in_db = self.check_email_already_in_db(email)
         if email_already_exist_in_db:
             raise EmailAlreadyExistInDb(
                 'Email given {} already exist, please choose something else'.format(email)  # nopep8
             )
         return True
 
-    def _check_email_already_in_db(self, email: str) -> bool:
+    def check_email_already_in_db(self, email: str) -> bool:
         """
         Verify if given email does not already exist in db
         """