micro-patch: add description to test-reports build target

[Bertrand Delacretaz]

Hi Solr gang,

Currently, build.xml says:

 <target name="test-reports">
   <!-- no description so it doesn't show up in -projecthelp ... yet -->

I think the test-reports target is worth a description:

 <target name="test-reports" description="generate HTML test reports">

(I found out when starting to write a patch for these reports ;-)

-Bertrand