tests: Fix date in archive logs

One archive log file was named nagios-01-04-2014-00.log
but had log entries dated 2013-12-31
Test for log entry search for specific times

This test exposes bug that apparently still persists

Affects issue #144
Fix: Parsers/GetLogEntries missing entries

Do not assume that log files are modified in
the correct order. Check every logfile for log
entries matching our date.

Fixes #144
Performance tweak in Pasers.get_log_entries

If start_time is provided as a search condition,
do not read files that are modified before start_time
Parsers - Better description for start_time
Merge pull request #151 from pynag/bugfix-log-entry-order2

Bugfix log entry order2