Allow to specify user_data in a template

For some cases relying on a script to be passed to shell
provisioner is not enough. So let's allow user to specify
actual userdata to be passed to the vm on creation, this
will help in complex scenarios like persistently changing
network routing that will survive reboots.

Sample configuration:

"user_data": "#cloud-config\nbootcmd:\n- ip route add 10.0.0.0/8 via 10.130.68.1 dev eth0"

builder/powervs/builder.go

@@ -103,6 +103,7 @@ func (b *Builder) Run(ctx context.Context, ui packer.Ui, hook packer.Hook) (pack
 		&StepCreateInstance{
 			InstanceName: b.config.InstanceName,
 			KeyPairName:  b.config.KeyPairName,
+			UserData:     b.config.UserData,
 		},
 		&communicator.StepConnect{
 			Config:    &b.config.RunConfig.Comm,

builder/powervs/common/run_config.go

@@ -40,6 +40,7 @@ type RunConfig struct {
 	InstanceName string   `mapstructure:"instance_name" required:"true"`
 	KeyPairName  string   `mapstructure:"key_pair_name" required:"true"`
 	SubnetIDs    []string `mapstructure:"subnet_ids" required:"false"`
+	UserData     string   `mapstructure:"user_data" required:"false"`
 	DHCPNetwork  bool     `mapstructure:"dhcp_network" required:"false"`
 	Source       Source   `mapstructure:"source" required:"true"`
 	Capture      Capture  `mapstructure:"capture" required:"true"`

builder/powervs/step_create_instance.go

@@ -2,6 +2,7 @@ package powervs
 
 import (
 	"context"
+	b64 "encoding/base64"
 	"fmt"
 	"time"
 
@@ -15,6 +16,7 @@ import (
 type StepCreateInstance struct {
 	InstanceName string
 	KeyPairName  string
+	UserData     string
 
 	doCleanup bool
 }
@@ -54,6 +56,7 @@ func (s *StepCreateInstance) Run(_ context.Context, state multistep.StateBag) mu
 		Processors:  core.Float64Ptr(0.5),
 		ServerName:  &s.InstanceName,
 		StorageType: *imageRef.StorageType,
+		UserData:    b64.StdEncoding.EncodeToString([]byte(s.UserData)),
 	}
 	ui.Message("Creating Instance")
 	ins, err := instanceClient.Create(body)