Docker builds fails if host doesn't have libparse-debianchangelog-perl installed

[ericriff]

As the title says, my host doesn't have libparse-debianchangelog-perl installed so I get

$ ./build.sh debian:buster
/bin/sh: 1: parsechangelog: not found
Traceback (most recent call last):
  File "./setup.py", line 41, in <module>
    pkg_version = subprocess.check_output("parsechangelog | grep ^Version:", shell=True)
  File "/usr/lib/python2.7/subprocess.py", line 223, in check_output
    raise CalledProcessError(retcode, cmd, output=output)
subprocess.CalledProcessError: Command 'parsechangelog | grep ^Version:' returned non-zero exit status 1

This is because build.sh relies on some setup.py commands to get the package name and version.
We should update the instructions to include installing this tool first.