Visibility rules for static members are different in Scala and Java, and this case requires an explicit static import. Even though these are Java files, they are run through scaladoc, which enforces Scala rules.

Also reverted the commit that reverts the upgrade to 2.11.6

Author: Iulian Dragos <jaguarul@gmail.com>

Closes #6260 from dragos/issue/scaladoc-false-error and squashes the following commits:

f2e998e [Iulian Dragos] Revert "[HOTFIX] Revert "[SPARK-7092] Update spark scala version to 2.11.6""
0bad052 [Iulian Dragos] Fix scaladoc faux-error.