[OWL-750][nqm-mng] Fix `TestAddNewAgent`
[OWL-750][nqm-mng] Fix `TestAddNewAgent`

The `TearDownTest` originally doesn't delete the `falcon_portal.host`
table in the MySQL. Now it's fixed.

Cepave/open-falcon-backend,masato25/open-falcon-backend,masato25/open-falcon-backend,Cepave/open-falcon-backend,masato25/open-falcon-backend,masato25/open-falcon-backend,Cepave/open-falcon-backend,masato25/open-falcon-backend,Cepave/open-falcon-backend,masato25/open-falcon-backend,Cepave/open-falcon-backend,Cepave/open-falcon-backend