[BUILD] added exclusion pattern for Saros Core

Ant4Eclipse / Eclipse compiler has problems with package-info.java
files. As those files are only needed for the document generation
exclude them in the compile process.

Change-Id: Icc3faa9ff9675d3d93109f4470243e0c38939a8a
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1364
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>