Refactor AugeasProviders::Provider

  * Extend the provider class
  * Provide a lens method
  * Provide a default_file method
  * Refactor the target method to use the default file
  * Refactor the augopen method to make it standard
Add a resource_path method to AugeasProviders::Provider
Accept blocks in AugeasProviders::Provider.augopen
augopen returns aug and path to block
Remove unused code in mailalias provider
Use augopen blocks in nrpe_command
Use augopen blocks in mounttab
Use augopen blocks in syslog
AugeasProviders::Provider: separate class/instance methods
Add AugeasProviders::Type to provide positionable
AugeasProviders::Provider: tests, tidyups and new instance methods
Condense all providers using new AugeasProviders::Providers helpers
Add YARD documentation to provider/type mixins
AugeasProviders::Provider: Add setvars, use $resource in puppet_auth provider
Fix provider_spec to call target twice
Fix ssh_config provider with standard resource_path accessor
Standardize apache_setenv provider
Fix provider_spec by not sending a string for a resource
AugeasProviders::Provider: Add standard definitions for exists? and destroy
AugeasProviders::Provider: Make resource_path default to target/name