Fix Debian service detection

* check_enabled now understands upstart (enough to
  check whether services start on boot)

* check_running now properly uses /usr/sbin/service
add npm to package provider
Add base commands helper (for test use mainly)
Separate build command method for testability and add custom path in this method
Add spec for build_command method
Add rake task for specs of heplers and backend
Remove adding default PATH

Error ``sorry, you are not allowed to set the following environment variables`` shows up with sudo secure_path setting.

So I've removed adding default PATH.
Merge pull request #133 from mizzy/add-custom-path

Add custom path to the command
Bump up version
Merge remote branch 'pr/132/head'
Bump up version
support lazy-evaluation options
add pre_command to Serverspec.options
add note for lazy options
Merge remote branch 'pr/134/head'
Working in progress
Serverspec::Configuration -> Serverspec.configuration
Serverspec.configuration.path and specs or it
Fix specs
Merge branch 'serverspec-configuration'