Configure parser cache databases in db-$realm file

Sam pointed out in Ia34a2e811 that the realm DB file is where you'd expect the
parser cache database hosts to be configured. He was right. Rather than
document the idiosyncracy, though, let's simply resolve it by moving the
configuration to where people expect it to be.

Change-Id: Icdaa4c1b5484ef6a361030e0954c6d334d0cdd5e