Add 3.6+ user authenticationRestrictions

[timvaillancourt]

This PR adds support for MongoDB user authenticationRestrictions, added in 3.6:

The authentication restrictions the server enforces on the created user. Specifies a list of IP addresses and CIDR ranges from which the user is allowed to connect to the server or from which the server can accept users.

https://docs.mongodb.com/manual/reference/method/db.createUser/#authentication-restrictions

Example user with authenticationRestrictions, post-change:

> db.system.users.find({},{_id:0, credentials:0}).pretty()
{
	"user" : "tim",
	"db" : "admin",
	"roles" : [
		{
			"role" : "root",
			"db" : "admin"
		}
	],
	"authenticationRestrictions" : [
		{
			"clientSource" : [
				"127.0.0.1"
			],
			"serverAddress" : [
				"127.0.0.1"
			]
		}
	]
}

If it's valuable I can add checks to confirm a valid IP or CIDR was passed as 'clientSource' or 'serverAddress', please let me know.

[szank]

Hi @timvaillancourt,
This looks like a great addition, and thank you for taking the time to implement it. It is really appreciated!

I have one remark though. Could you please add some unit tests for using the AuthenticationRestriction? The existing UpsertUser unit tests should be a good template.
A success and failure case unit tests would be greatly appreciated.

It will be a nice addition when it is merged :)

[szank]

Empty comment, I have put a proper comment in the issue page. Github won't let me leave an empty one.

[timvaillancourt]

Whoops, sounds good @szank. I will add unit tests shortly

[timvaillancourt]

@szank I've added a test for this. Please review, thanks

EDIT: I made a few more commits to clean up the way I wrote the tests. 100% done this time

[domodwyer]

Thanks @timvaillancourt !