Noisy log message when error while moving tablet

[danielmai]

What version of Dgraph are you using?

master

Have you tried reproducing the issue with the latest release?

yes

What is the hardware spec (RAM, OS)?

Ubuntu Linux

Steps to reproduce the issue (command/config used to run Dgraph).

When move tablets are running to different groups this can show up in the Zero log:

E0321 13:45:23.570754     346 raft.go:352] While applying tablet proposal: Tablet is already being served
github.com/dgraph-io/dgraph/dgraph/cmd/zero.init
	/home/ashish/projects/src/github.com/dgraph-io/dgraph/dgraph/cmd/zero/raft.go:161
runtime.doInit
	/home/ashish/go/src/runtime/proc.go:5222
runtime.doInit
	/home/ashish/go/src/runtime/proc.go:5217
runtime.doInit
	/home/ashish/go/src/runtime/proc.go:5217
runtime.doInit
	/home/ashish/go/src/runtime/proc.go:5217
runtime.doInit
	/home/ashish/go/src/runtime/proc.go:5217
runtime.main
	/home/ashish/go/src/runtime/proc.go:190
runtime.goexit
	/home/ashish/go/src/runtime/asm_amd64.s:1357

This doesn't stop the Zero but this log with the trace makes it look like an issue.

Expected behaviour and actual result.

The error message should say that the tablet is already being served and doesn't need to show the trace.

[lgalatin]

Fixed by #5333