Fix service resource on FreeBSD

The command:
puppet resource service puppet enable=true
will wrongly append to rc.conf:
puppet_enable_enable="YES"
What should be appended is:
puppet_enable="YES"
The regexp /(.*)(_enable)?=(.*)/ is wrong because the first (.*) consumes the _enable, which is then used as the rcvar_name.
Update freebsd_spec.rb
Merge pull request #1527 from robertomulabi/patch-1

Fix service resource on FreeBSD