Remove postinstall files matching exclude regex

Previous to this commit, postinstall files matching the provided exclude
regex were not removed from the postinstall list, but rather were just
prepended with '_'.  This caused an error since the script '_<original
filename>' doesn't exist in the definition.

This commit removes the files from the list of postinstall files if the
filename matches the provided regex

lib/veewee/provider/core/box/build.rb

@@ -119,7 +119,7 @@ def filter_postinstall_files(options)
           unless options["postinstall_exclude"].nil?
             options["postinstall_exclude"].each do |p|
               env.logger.info "Exclude pattern #{p}"
-              new_definition.postinstall_files.collect! { |f| f.match(p) ? f.gsub(/^/,"_"): f}
+              new_definition.postinstall_files.reject! { |f| f.match(p) }
             end
           end