Add proper contexts with timeouts for etcd operations (#7097)

This fixes an issue of perceived hang when incorrect
unreachable URLs are specified in MINIO_ETCD_ENDPOINTS
variable.

Fixes #7096

cmd/common-main.go

@@ -242,6 +242,7 @@ func handleCommonEnvVars() {
 					return &cert, terr
 				}
 			}
+
 			globalEtcdClient, err = etcd.New(etcd.Config{
 				Endpoints:         etcdEndpoints,
 				DialTimeout:       defaultDialTimeout,