docker: pass resource limitations in HostConfig
docker: pass resource limitations in HostConfig

While not documented anywhere, in Docker 1.6.0 the resource limits were
moved to HostConfig instead of Config.

BREAKING CHANGES:

  - Drops support for Docker versions before 1.6.0 (1.6.0+ is supported)

solarce/worker,travis-ci/worker,solarce/worker,travis-ci/worker,travis-ci/worker,solarce/worker