fix hdfs federation

[SelfEvoAI]

When hdfs use Federation will Exception:

09-25-2018 17:56:06 ERROR [Thread-6] com.linkedin.drelephant.ElephantRunner : getDefaultBlockSize on path `/' is not within a mount point
09-25-2018 17:56:06 ERROR [Thread-6] com.linkedin.drelephant.ElephantRunner : org.apache.hadoop.fs.viewfs.NotInMountpointException: getDefaultBlockSize on path `/' is not within a mount point
        at org.apache.hadoop.fs.viewfs.ViewFileSystem$InternalDirOfViewFs.getDefaultBlockSize(ViewFileSystem.java:928)
        at org.apache.hadoop.fs.viewfs.ViewFileSystem.getDefaultBlockSize(ViewFileSystem.java:658)
        at com.linkedin.drelephant.analysis.HDFSContext.load(HDFSContext.java:44)
        at com.linkedin.drelephant.ElephantRunner$1.run(ElephantRunner.java:101)
        at com.linkedin.drelephant.ElephantRunner$1.run(ElephantRunner.java:98)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:360)
        at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1900)
        at com.linkedin.drelephant.security.HadoopSecurity.doAs(HadoopSecurity.java:109)
        at com.linkedin.drelephant.ElephantRunner.run(ElephantRunner.java:98)
        at com.linkedin.drelephant.DrElephant.run(DrElephant.java:34)

[pralabhkumar]

Please log the error , instead of printStackTrace

[pralabhkumar]

I think its better to have 64MB as default (as thats HDFS default block size) . There should be property from the configuration file for defaultblocksize (or the path which is mounted instead of looking for / or /tmp), if getDefaultBlockSize gives exception then user provided default size can be taken (or other way round check if user have provided default block size , if not then go for getDefaultBlockSize and if that also gives exception then by default 64MB should be taken).