HBase backup: allow direct DistCP flag

HBase docs recommend that backups are done to cloud storage such as S3.

Internally, backup and restore relies on DistCP to copy files to backup storage. DistCP's docs mention the "-direct" parameter:

> Useful for avoiding potentially very expensive temporary file rename operations when the destination is an object store 

It looks useful to allow specifying this parameter for HBase backups, similar to how the YARN queue is also exposed.