Inserting random words on the command line stops the CLI from being parsed

Good behavior:

▶ livepeer -broadcaster -network offchain -foo=bar
flag provided but not defined: -foo
Usage of livepeer:
[snip]

Bad behavior:

▶ livepeer -broadcaster -network offchain random_nonsense -foo=bar
*-------------*------*
| Broadcaster | true |
*-------------*------*
I1031 18:09:17.953699   23455 starter.go:337] ***Livepeer is running on the offchain network***
I1031 18:09:17.956990   23455 starter.go:495] ***Livepeer is in off-chain mode***
[snip]

Actual flags on the far side of random_nonsense are ignored too:

▶ livepeer -network offchain random_nonsense -broadcaster
*
*
I1031 18:12:28.799456   23478 starter.go:337] ***Livepeer is running on the offchain network***
F1031 18:12:28.802987   23478 starter.go:460] No services enabled; must be at least one of -broadcaster, -transcoder, -orchestrator, -redeemer, -reward or -initializeRound

I suppose our CLI parsing library is seeing random_nonsense there as a subcommand? But we should be crashing if that's there, this can only cause bugs for people.