Connection exceptions can occur during configure_connection and can be retried.

https://bugzilla.redhat.com/show_bug.cgi?id=1120364

Add "connection not open" as another retryable connection exception.

Reported and patched by Carsten Clasohm
Don't crash exception translation w/ nil result attribute.

Exception.result is nil when attempting a query after PostgreSQL
disconnect, resulting in new exception:
NoMethodError: undefined method `error_field' for nil:NilClass
Add "database system is starting up" as retryable exception.

https://bugzilla.redhat.com/show_bug.cgi?id=1120364