host_name info is useful in several use cases including
1) to distinguish the concurrent tool invocations from the same user.
2) to understand the potential different performance from different hosts (e.g. local workstation VS cloudtop).
3) required to integrate the tool event log with the EPR system.
Test: atest tool_event_logger_test
Bug: 348482213
Change-Id: I98422b3f8ccec73d57fcdcdedac91780c448dc47
d067588a26