Don't create /var/log/nova.

Since we are using upstart for logs we should not be creating
/var/log/nova/* since it will be empty and just cause confusion.

Don't create /var/log/nova upon install and disable watchedfile logging
handler, since we use upstart to record stdout, and using that handler
creates an empty /var/log/nova/nova.log.

Change-Id: Ic1c71f01c226ec9d29a74ad41a80a9d368833979