Minor fixes for elkstack, bump ES to 1.3.3

# 2.1.0

- Bump elasticsearch to version 1.3.3. This should improve memory consumption and has a host of other bug fixes. See [release notes](http://www.elasticsearch.org/blog/elasticsearch-1-3-3-released/).

# 2.0.1

- Add log warning for when we are automatically generating lumberjack keypairs
- Updates to README about memory consumption and how to optimize it
- Moved variables around in agent to make intent more clear (no logic changes)