Add ability to connect to database server

[rmccue]

Requires humanmade/ssm#2 and changes to vantage-backend which I haven't shipped yet. Pushing early draft.

[joehoyle]

@rmccue how are you starting the SSM session? I assume you are starting it with a different document perhaps? Currently with the SSM PR too, I am not getting a handshake request

[joehoyle]

Ah I see https://github.com/humanmade/vantage-backend/pull/1547/files

[joehoyle]

I set this up locally, and I was running in to intermittent connection errors, specifically I was seeing an SSL handshake version mismatch error.

I logged all the recieved / sent data and ran a diff between times it worked and times it didn't which showed https://gist.github.com/joehoyle/116f96f917ea382b481b4a40ce52ede9/revisions. It seems the times it doesn't work, there's extra send packets from the ping interval. Once I commented out the setInterval for ping, I did not have connection errors.

Once connected I also haven't experienced any drops with the ping code removed.

@rmccue mentioned that the ping shouldn't interfere with the mysql connection, as presumably that's a different packet type or something long those lines, but it does seem like it is interfering. Could be that we are messing up state with packet etcs etc with a band implementation, or perhaps could be a ssm-server level issue too.