[UIMA-2101] fix test case to account for the fact that on some impl (varies by jdk / os ) the xml writer inserts or doesn't insert a new line before the first <Document> tag.  Before this fix, the test case passed on Windows / IBM Java 7 / 8, but failed on some linux systems (Jenkins).

git-svn-id: https://svn.apache.org/repos/asf/uima/uimaj/trunk@1588278 13f79535-47bb-0310-9956-ffa450edef68