Fix object auditor recon and logging

1. Nothing is logged until at least one audit needs more than log_time.
   If the audit runtime never exceeds this value (which is 3600 seconds
   by default) nothing is logged and the recon entry is never updated.
   It happens especially on very fast disks with a low usage and/or if
   only a few disks are audited (for example, using the --devices
   parameter on the command line).

   This patch changes this to log and update the recon cache entry
   at least one time after the first device audit.

2. If device_dirs is set the recon entry will be deleted after all
    devices are audited.

Change-Id: Ifa504d21389b3a5f7eaf914b19d6e26543dac121
Merge "Fix object auditor recon and logging"