Add extra option to devflow.conf file, containg a version_template file
for each package. Devflow will read this file, substitute all DEVFLOW_
variables and write it to version_file. The available variables are:
DEVFLOW_VERSION
DEVFLOW_DEBIAN_VERSION
DEVFLOW_BRANCH
DEVFLOW_REVISION_ID
DEVFLOW_REVISION_NUMBER
DEVFLOW_USER_EMAIL
DEVFLOW_USER_NAME