hblog: fixes in client, server, and list_hosts_of_tier

Summary:
* Made list_hosts_of_tier consistent and simpler. Esp. for -syslog and -gc
* Fix a bug when .hblogrc does not exist
* Fix a bug raises from hblogd when tailing unrecognized lines
* Remove erroneous double line breaks
* Don't open log files that are too small
* Fix server side bug that caused all log levels to be WARN
* Hexdiegest the md5sum, postpone truncating fingerprints until print