Making credentials optional for data sources

Username/password credentials are now optional
fields when creating a data source.  This is
possible because a fully updated sahara system
will use trusts to grant/revoke permissions
rather than passing around a username/password.

Change-Id: I7df556295e7e1b5c5e73230b294d4e8f8b7f05f3
Closes-Bug: #1367394
Merge "Making credentials optional for data sources"