Selected 2.5.2 and 2.6.0 hadoop versions
Added symlinks for the libhdfs versions 2.5.2 and 2.6.0
Added symlinks for the hadoop 2.5.2/2.6.0 configuration
Support hadoop 2.5.2/2.6.0 in the Travis hadoop installer
Added Hadoop version 2.5.2 and 2.6.0 to the Travis configuration file
Merge branch 'lastest_hadoop_versions_support' into develop