address telemetry log message locality

[bmc-msft]

Prior to this fix, all logging would show up as:

[2021-03-26T19:53:31Z INFO  onefuzz_telemetry] Starting libFuzzer crash report task

This moves the actual calls to log::log!() to the macros, which puts it in the source file in question.

Now the events look like:

[2021-03-26T21:20:14Z INFO  onefuzz_agent::tasks::report::libfuzzer_report] Starting libFuzzer crash report task

Most importantly, this allows us to use env_logger's ability to filter on a per module basis in a meaningful fashion. As an example, this allows:

RUST_LOG="info,onefuzz::syncdir=warn,onefuzz_agent::tasks::fuzz::libfuzzer=warn"