Avoid conflict with chef-sugar

sethvargo/chef-sugar imports an `installed?` into `Chef::Provider` at
runtime. This means as-it-stands a recipe importing chef-sugar recieves
an "ArgumentError: wrong number of arguments (0 for 1)" if it tries to
use the nodejs_npm resource.

This is unfortunate because it prevents me from using the npm resource
in a recipe that may run on hosts that don't already have npm installed.

If the cookbooks are compatible, I can use sugar's `compile_time`
(or `before`) context to make sure the node-installing recipes run
before `npm_list` gets called in the guard.

Without sugar, compile-time installation of node is much harder. Manual
use of `run_action` is possible, but complicated by the various paths
the nodejs recipes can take.

A name change here renders them compatible for this use.
Rename is_installed? to npm_package_installed?
Fix rubocop
Merge branch 'donaldguy-chef-sugar-compatibile'