Skip loading (and failing to load) lock files

Ignore lock files (and other hidden files) that zookeeper
will notify the jobboard about and avoid reading these as
potential jobs (which they are not).

Fixes bug 1312843

Change-Id: Ifa1ed31e22aed838f9baf883a6faaec00187663a
Merge "Skip loading (and failing to load) lock files"