Add cglib dependency to the Grails project test scope

This change addresses https://jira.grails.org/browse/GRAILS-11535

I tested this change by creating a new grails project. I ran "grails dependency-report". Then I made this change and ran "grails dependency-report" again. The only difference was the addition of these lines to the "test" scope:
```
+--- cglib:cglib:2.2.2
|    \--- asm:asm:3.3.1
````