Validate node version at runtime

[jbudz]

We get a decent number of issues filed relating to the wrong version of node running. At this time we make use of SSL constants that will cause issues in < 6, and there are some breaking changes in > 6 that will cause the process to fail. An early failure or warning would help with clearly identifying these errors.

[vedularaghu]

I'm a beginner in contributing to kibana. I'm planning to work on this issue. Do you want an early failure or warning?

[tylersmalley]

@mistic, can we close this?