LU-18799 utils: mount with maximum NIDs

LU-18799 utils: mount with maximum NIDs

Patch allows mount with maxumum NIDs in parameters.
- reserve space for mandatory mount options: 'device', etc.
- remove duplicate mgsnode list as parameter in mount options
- update 73b test to check mount is working too

Fixes: f9d346f0c1 ("LU-18587 utils: allow large NID lists in mount tools")
Signed-off-by: Mikhail Pershin <mpershin@whamcloud.com>
Change-Id: I46c296694a053c710310bced94ec95afae76b800
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58375
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>