Adding uaa.user.override property (matching master branch)

It has been important for dev environments to be able to override
user account details by changing the uaa.yml.  This change makes that
possible by default (rather than only adding accounts that are
missing it updates ones that are already there as well).
Merge pull request #17 from dsyer/feature/scimoverride

Adding uaa.user.override property (matching master branch)