changed HOURLY cron script to add logger use
Correcting su validation and tests when su => false

The su config option works differently than other logrotate config
options and does not have a corresponding 'nosu' version.  This adds
proper validation checks, tests and erb handling to allow for this.

Without this, it would be possible to have only 'su' in the logrotate
rule if no owner or group was specified.
Dodgy hack (downgrade rubygems) to get travis-ci builds working again
Ensure old config is removed when chaning to/from hourly rotation

When changing an existing rule to hourly, the config should be removed from
/etc/logrotate.d/. Similarly, when changing a rule from hourly, the config
should be removed from /etc/logrotate.d/hourly/.

Fixes #22