Previously, the code considered only a few of PGProperty names when creating a database connection. So there was no possibility to set the rest of the properties by passing them with build.properties or -D...

After the change, the code uses all the matching properties from System.properties, so we can increase test coverage.

For instance, the change adds tests with assumeMinServerVersion setting.

I still do not like how Properties contents is copied all over the place, however, we can't do better as we do not have Properties(List<Properties>) factory yet.

This test would have caught #3508 earlier.

The idea behind the change is:

• Prefer pgjdbc property names (the ones in PGProperty). For instance, previously, build.properties included a property named username which was handled in a special way since PGProperty.USER has a value of user.
  That is the reason I changed server to test.url.PGHOST which effectively means "use it as a default PGHOST value, and pass it via the URL rather than props object)
• host/port/database was handled separately when building the URL. Now the logic is that any property can be passed to the URL when building the URL with TestUtil. The test.url. prefix allows to configure which properties should be passed with the URL (TestUtil strips the prefix and adds the rest as a query parameter, etc)