hblog: Fix fd leak (Fixes #3)

Summary:
I noticed that hblog daemons were leaking file descriptors.
This fix explicitly closes files and the leak not longer happens.

It was more evident on tiers that had 1000s of
gc log files. There the hlogd would wold start having internal
errors saying "cannot open anymore files".

Test Plan:

    lsof | grep hblogd -c