Change Ia7415d2fbbb320f8eddc4e46c3a055414df5f997 removed per-image
logging from nodepool; it now keeps a series of named log files. The
"image" logger is removed, along with all the specific build logs.
I972a66f9c153f52df934d25ab2f77596bb2e5429 removed the
image_log_document_root argument; which wasn't doing anything in
nodepool::builder, but was actually being used to fill-out the
builder-logging.conf file. Thus we need this to not have a bad path
in the config file.
Change-Id: I6fdc3b622454b069f3ad2cf42da584d8df23a110
53ac2cfeae