Update AuthModule for AG-Security

With the release of AeroGear Security 1.0.1 we got rid of the AeroGearUser type.

This has an impact on code that is login in against it. The AeroGEarUser has/had a "username":
https://github.com/aerogear/aerogear-security/blob/1.0.0/src/main/java/org/jboss/aerogear/security/model/AeroGearUser.java#L26

This is gone, and the "replacement", the User/SimpleUser from AeroGEar (extends Agent) is using "loginName":
http://docs.jboss.org/picketlink/2/2.5.0.Beta3/api/org/picketlink/idm/model/Agent.html#getLoginName()

The Android library needs to reflect this change in here:
https://github.com/aerogear/aerogear-android/blob/master/src/org/jboss/aerogear/android/authentication/impl/AGSecurityAuthenticationModuleRunner.java#L102