[PDI-9568] Added JAAS external configuration and Kerberos keytab support configurable via VariableSpace (transformation/job properties).  (Being added for SP-1002)

Conflicts:
	src/org/pentaho/mongo/MongoUtils.java
Merge pull request #63 from brosander/SP-1002

[PDI-9568] Added JAAS external configuration and Kerberos keytab support...