This adds a new profile, `hadoop-2.6`, copying over the hadoop-2.4 properties, updating ZK to 3.4.6 and making the curator version a configurable option. That keeps the curator-recipes JAR in sync with that used in hadoop.

There's one more option to consider: making the full curator-client version explicit with its own dependency version. This will pin down the version from hadoop and hive imports

Author: Steve Loughran <stevel@hortonworks.com>

Closes #6191 from steveloughran/stevel/SPARK-7669-hadoop-2.6 and squashes the following commits:

e3e281a [Steve Loughran] SPARK-7669 declare the version of curator-client and curator-framework JARs
2901ea9 [Steve Loughran] SPARK-7669 Builds against Hadoop 2.6+ get inconsistent curator dependencies