LU-10327 test: use nogroup instead of nobody

LU-10327 test: use nogroup instead of nobody

In Ubuntu, there isn't any nobody group

Lustre-change: https://review.whamcloud.com/#/c/30559/
Lustre-commit: 6229a5ff318471fda18daceec79143007c4b204f

Change-Id: I2d4607b3d1384d2d619dd9640363533f92397356
Signed-off-by: Minh Diep <minh.diep@intel.com>
Reviewed-on: https://review.whamcloud.com/30772
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>
Reviewed-by: Jian Yu <jian.yu@intel.com>
Reviewed-by: John L. Hammond <john.hammond@intel.com>