postgresql: use postgres db instead of template1

In PostgreSQL template1 database is kind of special, as all new databases are
copied from it, when you do CREATE DATABASE. This implies a few restrictions:
e.g. you can't have more than one active session to template1, if one of them
tries to create a database. It will fail with:

    ERROR: source database "template1" is being accessed by other users

Using of postgres database instead of template1 resolves this issue.

Closes-Bug: #1355929

Change-Id: I8b1a36163984fbef6be66964456072d32da6a9d0
(cherry picked from commit 02fa15b4caaa414930b6ddf6a3a9fe8019751c26)
Merge "postgresql: use postgres db instead of template1" into stable/icehouse