To fix a bug in the retry logic caused when the auth token is cleared after receiving `ErrInvalidAuthToken` from the server and the subsequent call to `getToken` also fails due to some reason (eg. context deadline exceeded).
This leaves the client without a token and the retry will continue to fail with `ErrUserEmpty` unless the token is refreshed.
add 'FAIL:' to egrep
```shell
[root@LF-136-9 etcd]# egrep "(--- FAIL:|DATA RACE|panic: test timed out|appears to have leaked)" -B50 -A10 test-MTYyNjIyOTc0MQo.log
[root@LF-136-9 etcd]# egrep "(--- FAIL:|FAIL:|DATA RACE|panic: test timed out|appears to have leaked)" -B50 -A10 test-MTYyNjIyOTc0MQo.log
ok go.etcd.io/etcd/server/v3/auth 3.247s
ok go.etcd.io/etcd/server/v3/config 0.047s
ok go.etcd.io/etcd/server/v3/datadir 0.035s
ok go.etcd.io/etcd/server/v3/embed 1.944s
ok go.etcd.io/etcd/server/v3/etcdmain 0.326s
FAIL go.etcd.io/etcd/server/v3/etcdserver [build failed]
? go.etcd.io/etcd/server/v3/etcdserver/api [no test files]
ok go.etcd.io/etcd/server/v3/etcdserver/api/etcdhttp 0.110s
ok go.etcd.io/etcd/server/v3/etcdserver/api/membership 0.479s
ok go.etcd.io/etcd/server/v3/etcdserver/api/rafthttp 0.251s
ok go.etcd.io/etcd/server/v3/etcdserver/api/snap 0.045s
? go.etcd.io/etcd/server/v3/etcdserver/api/snap/snappb [no test files]
ok go.etcd.io/etcd/server/v3/etcdserver/api/v2auth 1.470s
ok go.etcd.io/etcd/server/v3/etcdserver/api/v2discovery 0.088s
ok go.etcd.io/etcd/server/v3/etcdserver/api/v2error 0.034s
ok go.etcd.io/etcd/server/v3/etcdserver/api/v2http 0.128s
ok go.etcd.io/etcd/server/v3/etcdserver/api/v2http/httptypes 0.033s
? go.etcd.io/etcd/server/v3/etcdserver/api/v2stats [no test files]
ok go.etcd.io/etcd/server/v3/etcdserver/api/v2store 0.068s
? go.etcd.io/etcd/server/v3/etcdserver/api/v2v3 [no test files]
? go.etcd.io/etcd/server/v3/etcdserver/api/v3alarm [no test files]
? go.etcd.io/etcd/server/v3/etcdserver/api/v3client [no test files]
ok go.etcd.io/etcd/server/v3/etcdserver/api/v3compactor 1.793s
? go.etcd.io/etcd/server/v3/etcdserver/api/v3election [no test files]
? go.etcd.io/etcd/server/v3/etcdserver/api/v3election/v3electionpb [no test files]
? go.etcd.io/etcd/server/v3/etcdserver/api/v3election/v3electionpb/gw [no test files]
? go.etcd.io/etcd/server/v3/etcdserver/api/v3lock [no test files]
? go.etcd.io/etcd/server/v3/etcdserver/api/v3lock/v3lockpb [no test files]
? go.etcd.io/etcd/server/v3/etcdserver/api/v3lock/v3lockpb/gw [no test files]
ok go.etcd.io/etcd/server/v3/etcdserver/api/v3rpc 0.089s
ok go.etcd.io/etcd/server/v3/etcdserver/cindex 0.045s
ok go.etcd.io/etcd/server/v3/lease 3.324s
ok go.etcd.io/etcd/server/v3/lease/leasehttp 2.096s
? go.etcd.io/etcd/server/v3/lease/leasepb [no test files]
? go.etcd.io/etcd/server/v3/mock/mockstorage [no test files]
? go.etcd.io/etcd/server/v3/mock/mockstore [no test files]
? go.etcd.io/etcd/server/v3/mock/mockwait [no test files]
ok go.etcd.io/etcd/server/v3/mvcc 8.805s
ok go.etcd.io/etcd/server/v3/mvcc/backend 1.983s
? go.etcd.io/etcd/server/v3/mvcc/backend/testing [no test files]
? go.etcd.io/etcd/server/v3/mvcc/buckets [no test files]
? go.etcd.io/etcd/server/v3/proxy/grpcproxy [no test files]
? go.etcd.io/etcd/server/v3/proxy/grpcproxy/adapter [no test files]
? go.etcd.io/etcd/server/v3/proxy/grpcproxy/cache [no test files]
ok go.etcd.io/etcd/server/v3/proxy/httpproxy 0.046s
ok go.etcd.io/etcd/server/v3/proxy/tcpproxy 0.035s
? go.etcd.io/etcd/server/v3/verify [no test files]
ok go.etcd.io/etcd/server/v3/wal 0.513s
ok go.etcd.io/etcd/server/v3/wal/walpb 0.045s
FAIL
FAIL: (code:2):
% (cd server && env go test -short -timeout=3m --race --cpu=16 ./...)
FAIL: 'unit' failed at Wed Jul 14 10:29:37 CST 2021
```
