Change the way role checks for default cluster

It should fix problems with PostgreSQL installation on Ubuntu.
Fix a typo
autopostgresqlbackup should use cluster version

If PostgreSQL cluster has specified version number, it will be used to
create autopostgresqlbackup scripts instead of the default version.
Revert "Change the way role checks for default cluster"

This reverts commit b00d1b2bb42b8da02d854360f83a4998e32b8487.
Merge pull request #3 from drybjed/default-cluster-fix

PostgreSQL fixes