Tailing edits should not update quota counts on ObserverNode

Currently in FSImage#loadEdits(), after applying a set of edits, we call

updateCountForQuota(target.getBlockManager().getStoragePolicySuite(), target.dir.rootDir);

to update the quota counts for the entire namespace, which can be very expensive. This makes sense if we are about to become the ANN, since we need valid quotas, but not on an ObserverNode which does not need to enforce quotas.

This is related to increasing the frequency with which the SbNN can tail edits from the ANN to decrease the lag time for transactions to appear on the Observer.