diotest4: Some code cleanup in diotest4.c

Signed-off-by: Xiong Zhou <xzhou@redhat.com>
Reviewed-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
diotest4: Skip some diotest4 cases on NFS

According to description of NFS and directIO in open(2), especially
"The Linux NFS client places no alignment restrictions on
O_DIRECT I/O", ignore "odd count"/"non-aligned" read-write FAILs
in diotest4.

Signed-off-by: Xiong Zhou <xzhou@redhat.com>
Reviewed-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
fcntl16: Skip fcntl16 test block2 and block3 on NFS

According to nfs(5), NLM supports advisory file locks only. So skip
fcntl16 test block 1 if NFS.

Signed-off-by: Xiong Zhou <xzhou@redhat.com>
Reviewed-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>