Accept an --all flags for `dcos cluster remove`
Accept an --all flags for `dcos cluster remove`

This flags removes all configured clusters.

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