RFR: 8281717: Cover logout method for several LoginModule

[Sibabrata Sahoo]

Added coverage to logout method.

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Commit messages:
 - 8281717: Cover logout method for several LoginModule

Changes: https://git.openjdk.java.net/jdk/pull/7940/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7940&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281717
  Stats: 49 lines in 1 file changed: 29 ins; 11 del; 9 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7940.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7940/head:pull/7940

PR: https://git.openjdk.java.net/jdk/pull/7940