FairScheduler handles "dots" in user names inconsistently in the config

A user name can contain a dot because it could be used as the queue name we replace the dot with a defined separator. When defining queues in the configuration for users containing a dot we expect that the dot is replaced by the "_dot_" string.
In the user limits we do not do that and user limits need a normal dot in the user name. This is confusing when you create a scheduler configuration in some places you need to replace in others you do not. This can cause issue when user limits are not enforced as expected.

We should use one way to specify the user and since the queue naming can not be changed we should also use the same "_dot_" in the user limits and enforce correctly.