Sets default encoding for PostgreSQL testing

Fixes the issue of some tests failing when inserting unicode characters
in the PostgreSQL test suite. This patch sets the default encoding of
all created databases to UTF8.

Related to blueprint sql-unit-tests-on-real-backend

Change-Id: Ie8629dd655ddb2327cce13c7e2a31cdb011791b5
Merge "Sets default encoding for PostgreSQL testing"