Reload bind only if config doesn't return any error

This new exec has to be called instead of service notification.
bind::zone - call new exec in order to reload bind process
uses validate_hash from puppetlabs stdlib module
New function: bind_check_hostname

This function is called from the default-record.erb in order to validate
each entry. This way, we can prevent bind configuration error.
default-record.erb now uses brand new function bind_check_hostname

This way, we can validate each record and avoid some nasty configuration
like "check-names warns", which should NOT be used.
zone-master.erb - removed ugly "check-names warn" directive
Merge PR16
Fix unit test in spec/defines/bind_zone_spec.rb