patching docker startup script for centos 7 (#37)
patching docker startup script for centos 7 (#37)

* patching docker startup script for centos 7

adding option `overlay2.override_kernel_check` in fallback plan for centos 7

* Simplification of the conditions for launching the docker in centos-7

* Adding link to docker guide as reference

iron-io/runner,iron-io/runner