This change adds project ID and bucket name columns to the generated
partner attribution report. Attribution values are now summed based on
their project ID and bucket name in addition to their user agent.
Additionally, the command to generate the attribution report has been
modified to optionally include only certain user agents.
Change-Id: I61a1d854379134f26b31467d9e83a787beb451dd
Attribution is attached to bucket usage, but that's more granular than
necessary for the attribution report. This change iterates over the
bucket attributions, parses the user agent, converts the first entry
to lower case, and uses that as the key to a map which holds the
attribution totals for each unique user agent.
Change-Id: Ib2962ba0f57daa8a7298f11fcb1ac44a8bb97875