Backups should be able to be restored to a separate filesystem

Adds a new withRestoreRootDir method to RestoreRequest. When specified, the bulk output will be sent to that directory rather than the value of hbase.fs.tmp.dir (which defaults to current user's home dir on current FS). You can pass a fully qualified URI to withRestoreRootDir, which allows the RestoreJob to save the output to a remote cluster if you've loaded the job's Configuration with the appropriate hdfs configs to connect to that cluster.