Add support for setting stacks when creating session (#138)

* Add support for setting stacks when creating session

* Add exec endpoint and move dns stuff to another package

* Rename command and status code

handlers/exec.go

@@ -0,0 +1,40 @@
+package handlers
+
+import (
+	"encoding/json"
+	"log"
+	"net/http"
+
+	"github.com/gorilla/mux"
+	"github.com/play-with-docker/play-with-docker/services"
+)
+
+type execRequest struct {
+	Cmd []string `json:"command"`
+}
+
+type execResponse struct {
+	ExitCode int `json:"status_code"`
+}
+
+func Exec(rw http.ResponseWriter, req *http.Request) {
+	vars := mux.Vars(req)
+	instanceName := vars["instanceName"]
+
+	var er execRequest
+	err := json.NewDecoder(req.Body).Decode(&er)
+	if err != nil {
+		rw.WriteHeader(http.StatusBadRequest)
+		return
+	}
+
+	code, err := services.Exec(instanceName, er.Cmd)
+
+	if err != nil {
+		log.Println(err)
+		rw.WriteHeader(http.StatusInternalServerError)
+		return
+	}
+
+	json.NewEncoder(rw).Encode(execResponse{code})
+}