Add default user_identity to logging record

Just like instance and color formatting parameters we can't assume that
the user_identity will always be in the logging record. This patch adds
a default value for it if missing to avoid exceptions.

Change-Id: Id02902adb2579d44f1f4f066757ef3855b5ece87
Closes-Bug: #1290503
Merge "Add default user_identity to logging record"