Support setting PROVIDE_ONLY for skipping cowbuilder stage
and BUILD_ONLY for skipping reprepro repository stage.
Drop REMOTE_REPOS configuration variable, as the name actually
doesn't reflect what the script supports nor is it of any use
in the main configuration file when having PROVIDE_ONLY and
BUILD_ONLY available.
This provides the base for using $job-source, $job-binaries and
$job-repos to get the build process scaling and distributed on
specific slaves.
Michael Prokop
Michael Prokop