Fix races / finally remove global app for good (#7570)

* finally remove global app for good

* test compilation fixes

* fix races

* fix deadlock

* wake up write pump so it doesn't take forever to clean up

api/admin_test.go

@@ -8,16 +8,11 @@ import (
 	"strings"
 	"testing"
 
-	"github.com/mattermost/mattermost-server/app"
 	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/store"
 	"github.com/mattermost/mattermost-server/utils"
 )
 
-func init() {
-	app.UseGlobalApp = false
-}
-
 func TestGetLogs(t *testing.T) {
 	th := Setup().InitSystemAdmin().InitBasic()
 	defer th.TearDown()