Add new script to run release builds. The script is heavily based upon
the release/generate-release.sh script by nwhitehorn.

This script can use optional configuration file to override defaults,
making running multiple serialzied builds with different specific
configurations or architecture-specific tunings quite easy.

Sample overrideable options are included in the release.conf.sample
file.

Approved by: kib (mentor)
MFC After: 2 weeks
X-MFC-To: stable/9 only