[SP-1266] Fix /kettle/runJob limited by the HTTP session timeout

 [SP-1266] Create repo connection for each remote job

If a job run via /kettle/runJob exceeds HTTP timeout, repository connection may be invalidated.
This fix creates a dedicated repo connection for each job using SlaveServerConfig.

http://jira.pentaho.com/browse/SP-1266
Backport of http://jira.pentaho.com/browse/PDI-11926