make generic HCFS as under filesystem; setup VM environment for under filesystem unit tests

This make generic HCFS as under filesystem.

The unit test environment for Cephfs and Glusterfs is created by vagrant, detailed information can be found at vagrant/{ceph,glusterfs}/README.md.

core-site.xml is generic hadoop configuration file. Most hadoop compatible filesystems (Ceph, glusterfs, s3, mapr, etc) use it to configure filesystem specific properties. 

Admittedly, it is formerly known as core-default.xml in hadoop 1.x