MongoDB - loopback.getCurrentContext() return null

loopback.getCurrentContext() return null after MongoDB call returns.

wrap up @Ichenay's patch https://github.com/lchenay/loopback/commit/f075c79 (see this comment for more details: https://github.com/strongloop/loopback/pull/337#issuecomment-61680577)

Fix #809
Also note that this is a server-side only test that should not be run in the browser. You need to use `describe.onServer()`.