Fix ECDSA test failures with JDK 1.8.


git-svn-id: https://svn.apache.org/repos/asf/santuario/xml-security-java/trunk@1602376 13f79535-47bb-0310-9956-ffa450edef68
Replacing some getChildNodes() calls

git-svn-id: https://svn.apache.org/repos/asf/santuario/xml-security-java/trunk@1602377 13f79535-47bb-0310-9956-ffa450edef68