Floss: Add log-output option for btmanagerd

Adds an option to output log to stderr instead of syslog.
This is useful when debugging btmanagerd while running it on terminal.

Bug: 228905413
Tag: #floss
Test: Manual - Ran `btadapterd -d --log-output=stderr`

Change-Id: Id35e172e9fa600a99b1a36d0ae80e51910fb667f