[SP-1229] Carte falls back to default repo

When executing a tranformation, carte may not be passed accurate paramters to connect to a repository.
Allow execution to continue with a default preconfigured repository.

http://jira.pentaho.com/browse/SP-1229

Backport of http://jira.pentaho.com/browse/PDI-11946
Merge pull request #498 from hudak/work.sp-1229

[SP-1229] Carte falls back to default repo