RFR 8050427 LoginContext tests to cover JDK-4703361

[Amanda Jiang]

Hi All,

Please be free to review these new tests for Dynamic configuration of 
authentication modules.

Bug: https://bugs.openjdk.java.net/browse/JDK-8050427
webrev:http://cr.openjdk.java.net/~amjiang/8050427/webrev.01/


Thanks,
Amanda