cmd,eth,server: add voting to CLI

[kyriediculous]

What does this pull request do? Explain your changes. (required)
This PR adds the option to vote from the CLI (for orchestrators) so that they don't have to export their keys.

Specific updates (required)

• generate poll contract abi bindings
• create a voteHandler for the new CLI server /vote endpoint
• add a Vote() method to LivepeerEthClient
• Add an option to the CLI to vote

How did you test each of these updates (required)
Added & ran unit tests
Ran workflow in CLI (except for testing with a live poll on rinkeby)

Does this pull request close any open issues?
Fixes #1447

Checklist:

• README and other documentation updated
• Node runs in OSX and devenv
• All tests in ./test.sh pass

Example

What would you like to do? (default = stats)
1. Get node status
2. View protocol parameters
3. List registered orchestrators
4. Invoke "initialize round"
5. Invoke "bond"
6. Invoke "unbond"
7. Invoke "rebond"
8. Invoke "withdraw stake" (LPT)
9. Invoke "withdraw fees" (ETH)
10. Invoke "claim" (for rewards and fees)
11. Invoke "transfer" (LPT)
12. Invoke "reward"
13. Invoke multi-step "become an orchestrator"
14. Set orchestrator config
15. Set Eth gas price
16. Get test LPT
17. Get test ETH
18. Sign a message
19. Vote on a poll
> 19
Enter the contract address for the poll you want to vote on> 0xf4e8Ef0763BCB2B1aF693F5970a00050a6aC7E1B
Identifier	Voting Options
0		Yes
1		No
2		Abstain
Enter the ID of the option you want to vote for> 0
Are you sure you want to vote "Yes" ? (y/n)> n
Identifier	Voting Options
0		Yes
1		No
2		Abstain
Enter the ID of the option you want to vote for> 2
Are you sure you want to vote "Abstain" ? (y/n)> n
Identifier	Voting Options
0		Yes
1		No
2		Abstain
Enter the ID of the option you want to vote for> 1
Are you sure you want to vote "No" ? (y/n)> y

 unable to submit vote transaction err=no contract code at given address

Enter the contract address for the poll you want to vote on> 0xbf790e51fa21e1515cece96975b3505350b20083
Identifier	Voting Options
0		Yes
1		No
2		Abstain
Enter the ID of the option you want to vote for> 1
Are you sure you want to vote "No" ? (y/n)> y

 success

I0422 03:30:44.191809   43457 backend.go:96]
******************************Eth Transaction******************************

Invoking transaction: "vote". Inputs: "_choiceID: 1"  Hash: "0xf6957c190f1f16fc2ca4a93846903eb435c5e08fa7f6f40b6e159aab6d74905f".

**************************************************************************

[kyriediculous]

Addressed the change requests in their respective fixup commits

fixup! cmd: add voting option to the CLI
00b49d6

fixup! server: CLI server voting handler
70c8b1c

fixup! eth: abigen for Poll contract
c385a51

[adamsoffer]

@kyriediculous @yondonfu do we want to include abstain as a choice in this first iteration? It's not currently accounted for in the spec defined in LIP-16, the subgraph, or the UI.

[yondonfu]

Left 2 minor comments.

Other than that, changes look good so feel free to address the comments when rebasing.

[yondonfu]

Can be shortened to if choice.IsValid() { ... }

[yondonfu]

Don't think we need the leading and trailing space as it will show up as:

 vote success

rather than

vote success

[kyriediculous]

Addressed the last comments and rebased

[yondonfu]

Looks like CI is failing:

eth/watchers/orchestratorwatcher_test.go:25:35: cannot use lpEth (type *eth.StubClient) as type eth.LivepeerEthClient in argument to NewOrchestratorWatcher:
	*eth.StubClient does not implement eth.LivepeerEthClient (wrong type for Vote method)
		have Vote("github.com/ethereum/go-ethereum/common".Address, *big.Int) error
		want Vote("github.com/ethereum/go-ethereum/common".Address, *big.Int) (*"github.com/ethereum/go-ethereum/core/types".Transaction, error)

[kyriediculous]

Apparently something went wrong in the rebase. Should be fixed.

I also added a test case for a CheckTx() error which should bring us to 100% coverage for the handler.

[yondonfu]

LGTM pending green CI