cgsnapshot: fix the print message when use cgsnapshot with -f

cgsnapshot: fix the print message when use cgsnapshot with -f

When use cgsnapshot with -f to save current configuration of cgroups,
the mount section is missing, this patch fix it.

the example as following:
# cgsnapshot -s -f config
        cpu = /cgroup/cpu;
# cat config
# Configuration file generated by cgsnapshot
mount {
}

group test {
        cpu {
                cpu.rt_period_us="1000000";
                cpu.rt_runtime_us="0";
                cpu.cfs_period_us="100000";
                cpu.cfs_quota_us="-1";
                cpu.shares="1024";
        }
}

Signed-off-by: Weng Meiling <wengmeiling.weng@huawei.com>
Acked-by: Ivana Hutarova Varekova <varekova@redhat.com>