Fix mesos urls

This was a bug I introduced in https://github.com/apache/incubator-spark/pull/71
Previously, we explicitly removed the mesos:// part; with PR 71, this no longer occured.
Merge pull request #94 from aarondav/mesos-fix

Fix mesos urls

This was a bug I introduced in https://github.com/apache/incubator-spark/pull/71.
Previously, we explicitly removed the mesos:// part; with #71, this no longer occurs.