Add property for CommandInfo URI's field.

[philwinder]

Can now upload files to the sandbox directory of a task. Working example:

spring.application.name=kibana
mesos.framework.name=kibana
mesos.resources.scale=3
mesos.resources.cpus=0.5
mesos.resources.mem=256
mesos.resources.ports=true
mesos.resources.ports.UI_5061=ANY
mesos.uri[0]=https://gist.githubusercontent.com/philwinder/773480c362663dde8411/raw/elasticsearch.yml
mesos.uri[1]=/etc/hosts

mesos.command=kibana --port=$UI_5061 --elasticsearch http://172.17.0.2:9200
mesos.docker.parameter.expose=$UI_5061
mesos.docker.network=BRIDGE
mesos.docker.image=kibana:latest

Which will download the gist and the /etc/hosts file and place them in the sandbox. Fixes #34

[philwinder]

LGTM