RBF: The construction of the trash path in the downstream nameservice should be based on src locations.

When deleting data to the Trash from a mount point, the Router should create trash path be consistent with downstream nameservice path.

Mount Table Entries:
Source             Destinations             
/tmp_ns1         ns1->/tmp    

hdfs dfs -rm -f /tmp_ns1/test

The downstream nameservice trash-path is  /user/xxx/.Trash/Current/tmp_ns1/test, should be /user/xxx/.Trash/Current/tmp/test.