The last line is to remove the previous version, since only the most recent version on a particular branch should be in the dist directory (older versions are archived automatically, see http://archive.apache.org/dist/bigtop/ and http://www.apache.org/dev/mirrors.html).
This page describes how to make a release of Apache Bigtop. Most of the content is shamelessly stolen from the the Whirr release process – thanks Whirr team!
Add the next version number (e.g. 0.2.0 after 0.1.0) to JIRA using this
In JIRA mark the released version as "released" on the "manage versions" page. Be sure to fill in a date if not already specified.