Improve log messages for EventLogging.

When I'm testing what events are transmitted and to what schemas, it can get
really confusing. This patch tweaks and standardises the log messages recorded
when EventLogging events take place, so that it's easier to see from logcat
what is being transmitted to where.

Change-Id: I03e92aecf4a5a056b65ffa89b01ad8336da34193
Merge "Improve log messages for EventLogging."