Convert buserver to libutil's logging

The primary motivation is to get automatic log rotation, but we
also get built-in locking for the logging calls.

This does have a side effect of changing the format used to print
timestamps in the log file.

While here, make helper routines for everything that takes a FILE *
to collect the entire structure's printout into a single buffer, and
then fwrite() that buffer all at once.  Only printDump really needs it,
as that logic would be shared between printing and logging, but it may
be useful in the future.

Garbage-collect the unused (and un-exported) printHashTable().

Change-Id: I860370e60082ea355806b3f1945eee76db7c32e3