Correcting JUnit XML output to conform Jenkins XSD

JUnit XML output, as understood by Jenkins, requires attribute
"timestamp" and not "timeStamp".

References:

- https://svn.jenkins-ci.org/trunk/hudson/dtkit/dtkit-format/dtkit-junit-model/src/main/resources/com/thalesgroup/dtkit/junit/model/xsd/junit-5.xsd
- http://svn.apache.org/repos/asf/ant/core/trunk/src/main/org/apache/tools/ant/taskdefs/optional/junit/XMLJUnitResultFormatter.java
- http://svn.apache.org/repos/asf/ant/core/trunk/src/main/org/apache/tools/ant/taskdefs/optional/junit/XMLConstants.java