Re-enable Marathon test
Re-enable Marathon test

It had been disabled in #1122, now that the Marathon version in DC/OS
contains the patch, the test can be re-enabled.

dcos/dcos-cli,kensipe/dcos-cli,kensipe/dcos-cli,kensipe/dcos-cli,dcos/dcos-cli,kensipe/dcos-cli,dcos/dcos-cli,kensipe/dcos-cli,dcos/dcos-cli,dcos/dcos-cli