LU-17000 utils: In mydaemon() check after calling open()

LU-17000 utils: In mydaemon() check after calling open()

This patch adds check after calling open() in function
mydaemon() instead of directly using the value

Test-Parameters: trivial kerberos=true testlist=sanity-krb5
CoverityID: 397666 ("Argument cannot be negative")
Fixes: d2d56f38da0 ("make HEAD from b_post_cmd3")
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: Ic59414977029221e8618c5bb3320e95d39d9cded
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53758
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Timothy Day <timday@amazon.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>