consensus: Reduce "non-deterministic signature" noise when using tmkms

[mdyring]

What happened:
When using tmkms against a single validator (but obviously also against multiple), the log is packed with

Apr 21 11:36:07 i-016ed17cbf9fe0bec gaiad[13908]: I[2019-04-21|11:36:07.288] Executed block                               module=state height=190523 validTxs=0 invalidTxs=0
Apr 21 11:36:07 i-016ed17cbf9fe0bec gaiad[13908]: I[2019-04-21|11:36:07.298] Committed state                              module=state height=190523 txs=0 appHash=2155AE6D685A2A78E7C3B702750528CDCAF466D7406185742D7F5F2275FDE796
Apr 21 11:36:07 i-016ed17cbf9fe0bec gaiad[13908]: E[2019-04-21|11:36:07.303] Error attempting to add vote                 module=consensus err="Existing vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 118810015DF9 @ 2019-04-21T11:36:06.95256089Z}; New vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 888D5294AEED @ 2019-04-21T11:36:06.885325351Z}: Non-deterministic signature"
Apr 21 11:36:07 i-016ed17cbf9fe0bec gaiad[13908]: E[2019-04-21|11:36:07.304] Error attempting to add vote                 module=consensus err="Existing vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 118810015DF9 @ 2019-04-21T11:36:06.95256089Z}; New vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 888D5294AEED @ 2019-04-21T11:36:06.885325351Z}: Non-deterministic signature"
Apr 21 11:36:07 i-016ed17cbf9fe0bec gaiad[13908]: E[2019-04-21|11:36:07.432] Error attempting to add vote                 module=consensus err="Existing vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 118810015DF9 @ 2019-04-21T11:36:06.95256089Z}; New vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 888D5294AEED @ 2019-04-21T11:36:06.885325351Z}: Non-deterministic signature"
Apr 21 11:36:07 i-016ed17cbf9fe0bec gaiad[13908]: E[2019-04-21|11:36:07.469] Error attempting to add vote                 module=consensus err="Existing vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 118810015DF9 @ 2019-04-21T11:36:06.95256089Z}; New vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 888D5294AEED @ 2019-04-21T11:36:06.885325351Z}: Non-deterministic signature"
Apr 21 11:36:07 i-016ed17cbf9fe0bec gaiad[13908]: E[2019-04-21|11:36:07.504] Error attempting to add vote                 module=consensus err="Existing vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 118810015DF9 @ 2019-04-21T11:36:06.95256089Z}; New vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 888D5294AEED @ 2019-04-21T11:36:06.885325351Z}: Non-deterministic signature"
Apr 21 11:36:07 i-016ed17cbf9fe0bec gaiad[13908]: E[2019-04-21|11:36:07.504] Error attempting to add vote                 module=consensus err="Existing vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 118810015DF9 @ 2019-04-21T11:36:06.95256089Z}; New vote: Vote{16:5B2ECC280D35 190523/00/2(Precommit) 695B9CC926DD 888D5294AEED @ 2019-04-21T11:36:06.885325351Z}: Non-deterministic signature"

What you expected to happen:
Less severe logging, after all Tendermint handles this gracefully.

Would recommend just logging with debug severity creating a special case for ErrVoteNonDeterministicSignature here

tendermint/consensus/state.go

Line 1519 in 671c5c9

if err == ErrVoteHeightMismatch {