SECURITY-769 AbstractServerLoginModule#validOptions

`AbstractServerLoginModule#validOptions` is initialized with the default
`HashSet` size (which is the default `HashMap`) size. However since it's
lazily initialized in `addValidOptions` and we have the valid module
options there we know what the right size will be.

 - change `AbstractServerLoginModule#addValidOptions` to initialize
   `validOptions` with the size of `moduleValidOptions`

Issue: SECURITY-769
https://issues.jboss.org/browse/SECURITY-769