change verbose [junit4:junit4] to just [junit4] and save horizontal space?

[Robert Muir]

i feel like this is a no-brainer, but there might be some regexps for
jenkins that could break or something else i'm not aware of:

Index: lucene/common-build.xml
===================================================================
--- lucene/common-build.xml    (revision 1497957)
+++ lucene/common-build.xml    (working copy)
@@ -869,6 +869,7 @@
         <mkdir dir="${tests.cachedir}/${name}" />

         <junit4:junit4
+            taskName="junit4"
             dir="@{workDir}"
             tempdir="@{workDir}/temp"
             maxmemory="${tests.heapsize}"