Remove unused $notify in check.pp

Currenlty its not possible to run the sensu puppet module with
puppet 3.6 because of a redelcaration of $notify in check.pp
This var was introduced with 62d7c948ca3ad8c16ab8aa5939dbaa69584f9f82
but is obsolete since a296283c193b166859d7390a23960346f6c12aa9 because
of the renaming.
plugin: Allow to retrieve plugin from URL

This PR aims to allow one to specify an url to retrieve plugins
from.
Remove default username for sensu

In some cases we need a passwordless sensu dashboard for different reasons, for example if we would like to manage the Auth using Nginx + Google_Auth_proxy[1].

Adding the default sensu user on the provider would mean that we have to authenticate everytime which doesn't make much sense.

[1] https://github.com/bitly/google_auth_proxy
several fixes for things that were botched on #200
Merge pull request #217 from misterdorm/pr200fixes

several fixes for things that were botched on #200
Merge pull request #214 from rhoml/rhoml/add-passwordless-dashboard

Remove default username for sensu
Merge pull request #212 from wywygmbh/unused_notify

Remove unused $notify in check.pp
Merge pull request #207 from Mylezeem/allow_url_plugins

plugin: Allow to retrieve plugin from URL
fixes one final bug from #200 / #217
Merge pull request #218 from misterdorm/pr217fixes

fixes one final bug from #200 / #217