cmd.go: Nicer error for unknown command

E.g.:

    [marca@marca-mac2 tsuru-client]$ ~/go/bin/tsuru target
    /Users/marca/go/bin/tsuru: "target" is not a tsuru command. See "tsuru help".

    Did you mean?
            target-add
            target-remove
            target-set
            target-list

    [marca@marca-mac2 tsuru-client]$ ~/go/bin/tsuru team
    /Users/marca/go/bin/tsuru: "team" is not a tsuru command. See "tsuru help".

    Did you mean?
            team-user-add
            team-remove
            team-create
            team-list
            team-user-list
            team-user-remove
Fuzzy string match for unknown command

plus display commands in order for easier human scanning and automated
testing
Add TestInvalidCommandFuzzyMatch01

and update TestCustomLookupNotFound
Add some more tests
Add TestInvalidCommandFuzzyMatch04
Merge pull request #1025 from msabramo/nicer_error_for_unknown_command

cmd.go: Nicer error for unknown command