Extend travis testing to test against postgres

This expands the test.sh script to accept a third element in T_TEST that
represents the database to test against.

We now launch a database (from travis services) and create a postgres db
when required.

Signed-off-by: Ken Barber <ken@bob.sh>
Merge pull request #730 from kbarber/maint/1.5.x/travis-postgres

Extend travis testing to test against postgres