Fix bug with remote states and implement secrets for remote state

I think I found a bug in the plugin, it looks for terraform.config for the remote configuration.
It should just be looking under the "config" key. Otherwise remote state configuration was being skipped.

Updated the documentation in the Dockerfile so that people can build this locally and test

Updated plugin.go -- Implemented exportSecrets
terraform remote configuration in some cases requires AWS credentials to grab the remote state, the current implementation did not allow for the secure use of those secrets.

Updated DOCS.md -- Adding documentation to use secrets for aws s3 remote configuration

DOCS.md

@@ -144,3 +144,26 @@ pipeline:
       app_version: 1.0.0
     parallelism: 2
 ```
+
+## Remote configuration
+
+If you are configuring an s3 remote state and require S3 environment secrets you add the secrets "FOO" and "BAR" to your drone environment and reference the secrets as follows. These will not be outputted to stdout.
+
+```yaml
+pipeline:
+  terraform:
+    image: jmccann/drone-terraform:0.5
+    plan: false
+    remote:
+      backend: S3
+      config:
+        bucket: my-terraform-config-bucket
+        key: tf-states/my-project
+        region: us-east-1
+    vars:
+      app_name: my-project
+      app_version: 1.0.0
+    secrets:
+      AWS_ACCESS_KEY_ID: FOO
+      AWS_SECRET_ACCESS_KEY: BAR
+```

Dockerfile

@@ -1,7 +1,7 @@
 # Docker image for Drone's terraform deployment plugin
 #
-#     CGO_ENABLED=0 go build -a -tags netgo
-#     docker build --rm=true -t plugins/drone-terraform .
+#     CGO_ENABLED=0 GOOS=linux GOARCH=amd64 go build -a -tags netgo
+#     docker build --rm=true -t jmccann/drone-terraform .
 
 FROM gliderlabs/alpine:3.2
 RUN apk-install ca-certificates git

main.go

@@ -4,8 +4,8 @@ import (
 	"encoding/json"
 	"os"
 
-	"github.com/joho/godotenv"
 	"github.com/Sirupsen/logrus"
+	"github.com/joho/godotenv"
 	"github.com/urfave/cli"
 )
 
@@ -90,7 +90,7 @@ func run(c *cli.Context) error {
 	}
 
 	remote := Remote{}
-	json.Unmarshal([]byte(c.String("terraform.remote")), &remote)
+	json.Unmarshal([]byte(c.String("remote")), &remote)
 
 	var vars map[string]string
 	if c.String("vars") != "" {

plugin.go

@@ -2,11 +2,11 @@ package main
 
 import (
 	"fmt"
+	"github.com/Sirupsen/logrus"
 	"github.com/aws/aws-sdk-go/aws/credentials"
 	"github.com/aws/aws-sdk-go/aws/credentials/stscreds"
 	"github.com/aws/aws-sdk-go/aws/session"
 	"github.com/aws/aws-sdk-go/service/sts"
-	"github.com/Sirupsen/logrus"
 	"io/ioutil"
 	"os"
 	"os/exec"
@@ -44,6 +44,9 @@ func (p Plugin) Exec() error {
 
 	var commands []*exec.Cmd
 	remote := p.Config.Remote
+	if len(p.Config.Secrets) != 0 {
+		exportSecrets(p.Config.Secrets)
+	}
 	if p.Config.Cacert != "" {
 		commands = append(commands, installCaCert(p.Config.Cacert))
 	}
@@ -93,6 +96,12 @@ func installCaCert(cacert string) *exec.Cmd {
 	)
 }
 
+func exportSecrets(secrets map[string]string) {
+	for k, v := range secrets {
+		os.Setenv(fmt.Sprintf("%s", k), fmt.Sprintf("%s", os.Getenv(v)))
+	}
+}
+
 func deleteCache() *exec.Cmd {
 	return exec.Command(
 		"rm",