[OWL-1730][nqm-mng] More tests for the data layer
[OWL-1730][nqm-mng] More tests for the data layer

Tests for `SelectNqmAgentByConnId()`

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