Worker registration logging fix

Author: Andrew Ash <andrew@andrewash.com>

Closes #608 from ash211/patch-7 and squashes the following commits:

bd85f2a [Andrew Ash] Worker registration logging fix

(cherry picked from commit c0795cf481d47425ec92f4fd0780e2e0b3fdda85)
Signed-off-by: Aaron Davidson <aaron@databricks.com>