Multiple playgrounds support (#215)

* Add Playground struct and basic support for creating it and retrieving
it

* Add missing functions in pwd mock

* Get playground from request domain and validate it exists. If valid set
it on the newly created session.

* Move playground specific configurations to the playground struct and use
it everytime we need that conf.

* Don't allow to specify a duration bigger that the allowed in the
playground

api.go

@@ -3,6 +3,7 @@ package main
 import (
 	"log"
 	"os"
+	"time"
 
 	"github.com/play-with-docker/play-with-docker/config"
 	"github.com/play-with-docker/play-with-docker/docker"
@@ -11,6 +12,7 @@ import (
 	"github.com/play-with-docker/play-with-docker/id"
 	"github.com/play-with-docker/play-with-docker/provisioner"
 	"github.com/play-with-docker/play-with-docker/pwd"
+	"github.com/play-with-docker/play-with-docker/pwd/types"
 	"github.com/play-with-docker/play-with-docker/scheduler"
 	"github.com/play-with-docker/play-with-docker/scheduler/task"
 	"github.com/play-with-docker/play-with-docker/storage"
@@ -41,6 +43,16 @@ func main() {
 
 	sch.Start()
 
+	d, err := time.ParseDuration(config.DefaultSessionDuration)
+	if err != nil {
+		log.Fatalf("Cannot parse duration %s. Got: %v", config.DefaultSessionDuration, err)
+	}
+
+	playground := types.Playground{Domain: config.PlaygroundDomain, DefaultDinDInstanceImage: config.DefaultDinDImage, AllowWindowsInstances: config.NoWindows, DefaultSessionDuration: d, AvailableDinDInstanceImages: []string{config.DefaultDinDImage}}
+	if _, err := core.PlaygroundNew(playground); err != nil {
+		log.Fatalf("Cannot create default playground. Got: %v", err)
+	}
+
 	handlers.Bootstrap(core, e)
 	handlers.Register(nil)
 }