LUCENE-5881: Add "beasting" of tests: repeats the whole "test" Ant target N times with "ant beast -Dbeast.iters=N"

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1617078 13f79535-47bb-0310-9956-ffa450edef68
LUCENE-5881: Add parameter check, beautify some other groovy code

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1617079 13f79535-47bb-0310-9956-ffa450edef68