test: flaky light client test

[erikgrinaker]

Had a spurious test failure, this is all the logs said:

2021/01/27 19:25:46 all witnesses have either not responded, don't have the blocks or sent invalid blocks. 
	You should look to change your witnesses or review the light client's logs for more information
FAIL	github.com/tendermint/tendermint/light	170.857s

[cmwaters]

Do you know what test it was? I will see if I can reproduce it

[erikgrinaker]

No, this was everything the logs contained. I've seen a couple of other flaky light client tests as well. You can try running this until something fails:

$ while go test -v -count 1 -race ./light/...; do true; done