utsname() can return NULL while process is exiting. Kernel releases
file locks during process exits. We send request to mds when releasing
file lock. So it's possible that we open mds session while process is
exiting. utsname() is called in create_session_open_msg().

Link: http://tracker.ceph.com/issues/21275Signed-off-by: N"Yan, Zheng" <zyan@redhat.com>
Reviewed-by: NJeff Layton <jlayton@redhat.com>
[idryomov@gmail.com: drop utsname.h include from mds_client.c]
Signed-off-by: NIlya Dryomov <idryomov@gmail.com>