The error states that the HDFS path /user is writable only by HDFS user and not by root.
As the permission is set as 755 for /user. If you want to run the sqoop command as root, you would need to grant write access to root user which would be 757.
I.e. Owner would have read,write,execute access. Group would have read and execute and other users would have read, write and execute.
If you do not want to change the permission for the /user folder, then try running the sqoop command with hdfs user as the user has complete access to the /user hdfs filesystem path.
Hope this helps.