Fix coverity defects

1.coverity scan CID:147445 function zfs_do_send in zfs_main.c
Buffer not null terminated (BUFFER_SIZE_WARNING)

2.coverity scan CID:147443 function zfs_do_bookmark in zfs_main.c
Buffer not null terminated (BUFFER_SIZE_WARNING)

3.coverity scan CID:147660 function main in zinject.c
Passing string argv[0] of unknown size to strcpy
By the way, the leak of g_zfs is fixed.

4.coverity scan CID: 147442 function make_disks in zpool_vdev.c
Buffer not null terminated (BUFFER_SIZE_WARNING)

5.coverity scan CID: 147661 function main in dir_rd_update.c
passing string cp1 of unknown size to strcpy

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: luozhengzheng <luo.zhengzheng@zte.com.cn>
Closes #5130