tiup ctl etcd doesn't work without extra steps

[dveeden]

Bug Report

tiup uses etcdctl version 3.3.10 which defaults to etcctl API v2, which doesn't work with PD v6.3.0.

https://etcd.io/docs/v3.5/dev-guide/interacting_v3/ says:
"By default, etcdctl on master (3.4) uses the v3 API and earlier versions (3.3 and earlier) default to the v2 API."

$ tiup ctl:v6.4.0 etcd | grep -A2 WARNING
Starting component `ctl`: /home/dvaneeden/.tiup/components/ctl/v6.4.0/ctl etcd
WARNING:
   Environment variable ETCDCTL_API is not set; defaults to etcdctl v2.
   Set environment variable ETCDCTL_API=3 to use v3 API or ETCDCTL_API=2 to use v2 API.

$ find ~/.tiup -name etcdctl -print -exec {} -version \;
/home/dvaneeden/.tiup/components/ctl/v6.3.0/etcdctl
etcdctl version: 3.3.10
API version: 2
/home/dvaneeden/.tiup/components/ctl/v6.4.0/etcdctl
etcdctl version: 3.3.10
API version: 2

Two possible solutions:

1. Set the ETCDCTL_API variable to 3
2. Upgrade etcdctl to the latest version.

[dveeden]

Example with TiDB:

$ ETCDCTL_API=3 tiup ctl:v6.4.0 etcd get --prefix /topology/grafana --print-value-only | jq .
Starting component `ctl`: /home/dvaneeden/.tiup/components/ctl/v6.4.0/ctl etcd get --prefix /topology/grafana --print-value-only
{
  "ip": "127.0.0.1",
  "port": 3000,
  "binary_path": "/home/dvaneeden/.tiup/components/grafana/v6.3.0/bin/grafana-server"
}