elodina/exhibitor-mesos-framework task runner

Implemented to run elodina/exhibitor-mesos-framework. Exposes stack variables:

• $app.host - elodina/exhibitor-mesos-framework scheduler address.
• $app.port - elodina/exhibitor-mesos-framework scheduler port.
• $app.api - elodina/exhibitor-mesos-framework scheduler api address in a form http://$host:$port.
• $app.exhibitor-$id - Zookeeper connection endpoint in a form $host:$port
• $app.zkConnect - comma separated connection string for all known Zookeeper nodes.

For $app == exhibitor that has Exhibitor nodes 0 and 1 variables would be:

• exhibitor.host, exhibitor.port and exhibitor.api for scheduler.
• exhibitor.exhibitor-0 and exhibitor.exhibitor-1
• exhibitor.zkConnect