Add dockerfiles to repo.
Update build_docker.sh and add instructions for building Docker images.
Add Docker usage example
Better emphasis on sections being files
Fix docker image tag
build_docker.sh: Exit on first failed command
Full heka+docker example
Dont name intermediary container for build
Grammar changes
Verify sha1sums in docker
Update Changelog with Docker changes
Use debian base image, to reduce size
Use COPY not ADD
Fix review items
Merge pull request #1067 from ecnahc515/dockerfile

Add Dockerfile(s) to Heka repo.
Move hekad config into pipeline config.

Watch for signals in separate go routine.
Split up pipeline startup into multiple functions
Remove udp from test configs which don't need it

Fixes intermittent test failure caused by plugins loading UDP and not cleaning
up.
SIGHUP Reloads config, and recreates all plugins
Add pipeline/net.go

Includes basic watching of net.Listeners