fix default for ROCK_CI_CONFIG_DIR
review and clean rock-ci-build

 - update environment variable to have the ROCK_CI_ prefix
 - remove handling of envvars that are now part of rock_ci_setdefaults
 - remove the documentation generation stuff, it will have to have
   its own script now
 - rename the successful flag to build-successful as we will
   create other for other operations (e.g. doc-successful)