Dev userdata

Added a new feature in CS to allow users or system admin to pass their user data scripts onto virtual machines then execute them. Users can specify their comma-separated user data scripts in VMUserData parameter in their JDL. They must be accessible via HTTP. Similarly, CS system admin can also specify user data script to run on all virtual machines created by CS using default_VMUserData parameter in cloud_scheduler.conf. These scripts specified in default_VMUserData must be local files.