environs: add machineNonce to StartInstance()

environs/dummy/environs.go

 // The dummy provider implements an environment provider for testing
 // purposes, registered with environs under the name "dummy".
 //
 // The configuration YAML for the testing environment
 // must specify a "state-server" property with a boolean
 // value. If this is true, a state server will be started
 // the first time StateInfo is called on a newly reset environment.
 //
 // The configuration data also accepts a "broken" property
 // of type boolean. If this is non-empty, any operation
@@ skipping 546 matching lines @@
 }
 
 func (e *environ) StartInstance(machineId, machineNonce string, series string, cons constraints.Value, info *state.Info, apiInfo *api.Info) (environs.Instance, error) {
         defer delay()
         log.Infof("environs/dummy: dummy startinstance, machine %s", machineId)
         if err := e.checkBroken("StartInstance"); err != nil {
                 return nil, err
         }
         e.state.mu.Lock()
         defer e.state.mu.Unlock()
+        if machineNonce == "" {
+                return nil, fmt.Errorf("cannot start instance: missing machine nonce")
+        }
         if _, ok := e.Config().CACert(); !ok {
                 return nil, fmt.Errorf("no CA certificate in environment configuration")
         }
         if info.Tag != state.MachineTag(machineId) {
                 return nil, fmt.Errorf("entity tag must match started machine")
         }
         if apiInfo.Tag != state.MachineTag(machineId) {
                 return nil, fmt.Errorf("entity tag must match started machine")
         }
         if strings.HasPrefix(series, "unknown") {
@@ skipping 212 matching lines @@
 // time.Durations into this value.
 var providerDelay time.Duration
 
 // pause execution to simulate the latency of a real provider
 func delay() {
         if providerDelay > 0 {
                 log.Infof("environs/dummy: pausing for %v", providerDelay)
                 <-time.After(providerDelay)
         }
 }