Build should support cross compile of hadoop distros

[kkasravi]

Right now we have a mix of pure hadoop versions and some cloudera version.
The opportunities to have version mismatches is high.
We should support hortonworks, cloudera, etc as well as pure apache open source.

Runtime should also be able to target different distro's - for example when setting
classpath and other environment variables for the executors.

[clockfly]

We will move hadoop dependency out of core.