Simplify docker publish plugin
Fixing session section of readme
Exit app if config cannot be read correctly
Merge pull request #595 from epipho/session-duration

Fixing session section of readme
Merge pull request #596 from epipho/config-error

Exit app if config cannot be read correctly
minor session refactoring in prep for upcoming changes discussed in #590
Merge pull request #598 from bradrydzewski/master

minor session refactoring in prep for upcoming changes discussed in #590
Merge pull request #591 from scrapinghub/docker-host

Use well known DOCKER_HOST syntax for Docker publish
Merge