1, add a new mode to run on existing environment
2, adjust the output line format
3, make the way to run mkdef be compatible with old release
4, add PERF_CSV_CHAR variable to control the delimiter used in CSV report
- refine the xcatperftest tool to make it be easily integrated into xcattest
- add testcase/performance/.. to trigger the performance testcase
- fix manpage missing issue for xcatperftest
* Feature #2681, to add a script in xCAT-test to get the performance baseline for node range operation.
* adopt review comments in PR#2916:
1, add the rst file for xcatperftest (#2681)
2, using /bin/bash as script executor
3, FILES in manpage should not be in the same line
4, minor adjustment if PERF_NOCREATE/PERF_DRYRUN is set
