No support for passing options in mongdb node

[thobhanifreddy]

I was trying to pass allowDiskUse = true. I asked question on stackoverflow and realised there is no way I pass options.

[thobhanifreddy]

I have edited code enough that allowDiskUse = true works(at least for me). Not sure if I should PR for that!

[hardillb]

If you think it would be useful for others, raise a pull request and we'll have a look at it.

Please also make sure you have read the Contributing.md docuent in the root of this project.

[thobhanifreddy]

I tried adding allowDiskUse option but my PR fails The Travis CI build test. I am not sure what does that mean!