Fix dependency on /etc/clamav/scans for the Scan resource

To ensure /etc/clamav/scans exists prior to creating a file, this makes
clamav::scan include the base class and requires it for the scan file.
I've also added a few tests for the default parameters.
Merge branch 'scan_require' of https://github.com/lamawithonel/puppet-clamav into lamawithonel-scan_require
Merge branch 'lamawithonel-scan_require'