[PDI-10591]: NPE and exposed exception on the DI-Server/Carte status page when the repository is not correctly defined (or repositories.xml is not accessible) - exception is not logged in the pentaho.log nor any tomcat\logs

The fix consists of two minor changes:
1)In the case when the repository is not correctly defined (or repositories.xml is not accessible) the page will display the short message: Unable to connect to repository:<Repository_Id>;
2)Added logging for the exception (with full stacktrace ) into pentaho.log

There is no any changes in logic of processing data in GetStatusServlet just minor tune so there is no need in unit tests.
Merge pull request #653 from stepanovdg/PDI-10591

[PDI-10591]: NPE and exposed exception on the DI-Server/Carte status pag...