Poor error message when passing beacon node command line option to `deposit` command

[arnetheduck]

It looks like parsing of --tcp-port locks the command-line parser into thinking it's running without a specific command

[arnetheduck@praeceps nimbus-eth2]$ build/nimbus_beacon_node --network=mainnet --data-dir=/tmp deposits
The required option 'depositsCmd' was not specified
Try nimbus_beacon_node --help for more information.
[arnetheduck@praeceps nimbus-eth2]$ build/nimbus_beacon_node --network=mainnet --data-dir=/tmp --tcp-port=2000 deposits
The command 'noCommand' does not accept arguments
Try nimbus_beacon_node --help for more information.

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