status/rest: Use utils.get_log_entries internally
Make log access configurable

This patch creates a new setting 'enable_local_logs' which
if set to false will disable all reading of log files.

This will help in cases like #495 where log access is a supposed
CPU hog for the adagios interface, and makes it simple to turn log
access off when troubleshooting performance issues.

Also affects issue #503 as one part of solving top_alert_producer issues.