New feature: Added ability to enable/disable logrotate

I some cases logrotate should be configurable with an other puppet module
like https://github.com/rodjek/puppet-logrotate.
To solve this problem an additional parameter 'enable_logrotate' (default
true) was added.
Merge remote-tracking branch 'upstream/master' into feature/dol-enable-disable-logrotate
Added tests for enable_logrotate
Merge pull request #1 from Jimdo/feature/dol-enable-disable-logrotate

Added some tests
Merge pull request #59 from dol/feature/dol-enable-disable-logrotate

New feature: Added ability to enable/disable logrotate