change run signatures

Run now takes a context as well as a statebag. We'll assign the context
to the blank identifier to prevent namespace collisions. We'll let the
step authors opt-in to using the context.

`find . -iname "step_*.go" -exec gsed -i'' 's/func \(.*\)Run(/func \1Run(_ context.Context, /' {} \;`

builder/cloudstack/step_create_instance.go

@@ -27,7 +27,7 @@ type stepCreateInstance struct {
 }
 
 // Run executes the Packer build step that creates a CloudStack instance.
-func (s *stepCreateInstance) Run(state multistep.StateBag) multistep.StepAction {
+func (s *stepCreateInstance) Run(_ context.Context, state multistep.StateBag) multistep.StepAction {
 	client := state.Get("client").(*cloudstack.CloudStackClient)
 	config := state.Get("config").(*Config)
 	ui := state.Get("ui").(packer.Ui)