LU-15913 tests: fix set_params_xxx

LU-15913 tests: fix set_params_xxx

Move argument number check from set_params_(clients|mdts|osts)
to set_params_nodes. Without that fix these functions
didn't set (MDS|OSS|CLIENT)_LCTL_SETPARAM_PARAM when
the number of nodes was < 2.

Test-Parameters: trivial
Fixes: 9a1d68f9b8 ("LU-15913 tests: add rename stress test via racer")
Signed-off-by: Sergey Cheremencev <scherementsev@ddn.com>
Change-Id: I0733109c53cdea435b4461da7ac44e54fa49498c
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/55143
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Deiter <adeiter@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>