(PDB-577) Lower KahaDB MessageDatabase logging threshold.

- Previously, premature termination of PuppetDB import under specific ownership
conditions led to a residual KahaDB lock file that could prevent subsequent imports
from running with no obvious reason why.  This patch lowers the log threshold
for KahaDB MessageDataBase so affected users are informed.
Merge pull request #991 from wkalt/ticket/master/pdb-577-KahaDB-lock-file-broker-failure

(PDB-577) Lower KahaDB MessageDatabase logging threshold.