added attribute "tests" to testsuite as the number of tests in the suite

This is required to use the xsl file with the Jenkins xUnit plugin
and to be compliant with junit-4.xsd, see
https://svn.jenkins-ci.org/trunk/hudson/dtkit/dtkit-format/dtkit-junit-model/src/main/resources/com/thalesgroup/dtkit/junit/model/xsd/junit-4.xsd

ctest_valgrind_to_junit.xsl

@@ -3,6 +3,9 @@
 
   <xsl:template match="/Site">
       <testsuite name="ValgrindTests">
+        <xsl:attribute name="tests">
+          <xsl:value-of select="count(/Site/DynamicAnalysis/Test)"/>
+        </xsl:attribute>
 	<properties>
 	  <xsl:for-each select="@*">
 	    <property>