RFR 8151352, jdk/test/sample fails with "effective library path is outside the test suite"

[Felix Yang]

Hi all,
    please review the fix for two tests under "test/sample/".

Bug:
     https://bugs.openjdk.java.net/browse/JDK-8151352
Webrev:
     http://cr.openjdk.java.net/~xiaofeya/8151352/webrev.00/

Original declaration, "@library ../../../src/sample...", is invalid with 
the latest change in jtreg. See 
https://bugs.openjdk.java.net/browse/CODETOOLS-7901585. This fix doesn't 
resolve dependency to "src/sample", but only converts them into testng 
tests and declares "external.lib.roots" to avoid dot-dot.

Thanks,
Felix