rose config_cli: style changes

Style changes made as follows:
 * NoMedata event added
 * os.path.abspath(rel_path) used instead of cwd + "/" + rel_path
 * os.path.join used
 * POpen and Reporter used
 * System exits rather than returning None when both files and meta-key are used
 * os.sep used where "/" was previously used in setting up rel_path
 * older %s formatting used for making message to be consistent with usage later on