Adjust AzDO feed pattern to accommodate dnceng-stage

[jonfortescue]

Currently the AzDoNuGetFeedPattern regex doesn't expect hyphens in the account name and thus fails when attempting to publish to dnceng-stage (see error here).

This fixes that.

To double check:

• The right tests are in and and the right validation has happened. Guidance: https://github.com/dotnet/core-eng/tree/master/Documentation/Validation