Log understandable error when the developer has forgotten a provider parameter

[jbeurel]

https://github.com/moooink/loopback-component-satellizer/blob/master/lib/facebook/index.js#L26

"Cannot read property 'private' of undefined","stack":"TypeError: Cannot read property 'private' of undefined\n  at fetchAccessToken (/home/user/project/node_modules/loopback-component-satellizer/lib/facebook/index.js:26:35