This is a patch to build a centos image to support installing DC/OS as
a magnum coe.
Two elements are included: dcos and docker, only used to build a centos
image.
1. Element docker will install and configure docker in centos.
2. Element dcos will download dcos_generate_config.sh and do some
configurations for DC/OS.
Design spec in contrib/drivers/dcos_centos_v1/image/README.md.
Partially-Implements: blueprint mesos-dcos
Change-Id: I30fa4c102205aa2475b9491398c06da0d1e86f84
10e9132bb8