Remove on suspend option

Hi,

first of all thanks for this plugin, I was looking for a solution to manage the host entries, and so far it seems to work very good.

I found one issue so far: When you call `vagrant suspend` the host entries are removed, but when calling `vagrant resume` they are not added again.

So I made some little changes to fix this, please consider pulling them:

- host entries are not removed by default when calling `vagrant suspend`
- added an option to remove them on suspend when you want it
- always check if host entries need to be added when calling `vagrant resume`