Fix TestConnectionUtils to py3x compatibility

Tests in TestConnectionUtils class depends on database and DB connector,
so the simplest way to run them with python 3.X is to use same database
and connector for the both python versions. PostgreSQL and psycopg2 are
looks good for this.

Replaced ``mysql`` to ``postgresql`` in TestConnectionUtils.

Change-Id: Icb1d6324b58feed515e4eb885715cbf2195768cf
Merge "Fix TestConnectionUtils to py3x compatibility"