RBF: Improve the use of setQuota command

If hdfs dfsrouteradmin -setQuota only set one of -nsQuota and -ssQuota, the another one will be cleared.
The following is the step:
1. set /test1 -nsQuota 400 -ssQuota 200
hdfs dfsrouteradmin -setQuota /test1 -nsQuota 400 -ssQuota 200
Successfully set quota for mount point /test1

2. after a moment, list /test1, everything is ok.
hdfs dfsrouteradmin -ls /test1
Source Destinations Owner Group Mode Quota/Usage
/test1 ns1->/test1 hadp hadp rwxr-xr-x [NsQuota: 400/0, SsQuota: 200 B/0 B]

3. only set /test1 -nsQuota 600
hdfs dfsrouteradmin -setQuota /test1 -nsQuota 600
Successfully set quota for mount point /test1

4. after a moment, list /test1, now ssQuota has been cleared.
hdfs dfsrouteradmin -ls /test1
Source Destinations Owner Group Mode Quota/Usage
/test1 ns1->/test1 hadp hadp rwxr-xr-x [NsQuota: 600/0, SsQuota: -/-]

HDFS-13307.001.patch