api: add helper Dialer implementations

To disable SSL by default we want to transfer
`OpenSslDialer` to the go-openssl repository.
In order to do so, we need to minimize the amount of
copy-paste of the private functions.

`AuthDialer` is created as a dialer-wrapper, that
calls authentication methods.
`ProtoDialer` is created to receive and check the `ProtocolInfo`
in the created connection.
`GreetingDialer` is created to fill the `Greeting`
in the created connection.

Part of #301

Author: DerekBum

CHANGELOG.md

@@ -37,6 +37,11 @@ Versioning](http://semver.org/spec/v2.0.0.html) except to the first release.
   the response (#237)
 - Ability to mock connections for tests (#237). Added new types `MockDoer`,
   `MockRequest` to `test_helpers`.
+- `AuthDialer` type for creating a dialer with authentication (#301)
+- `ProtocolDialer` type for creating a dialer with `ProtocolInfo` receiving and 
+  check (#301)
+- `GreetingDialer` type for creating a dialer, that fills `Greeting` of a
+  connection (#301)
 
 ### Changed
 

connection.go

@@ -440,7 +440,9 @@ func (conn *Connection) dial(ctx context.Context) error {
 	}
 
 	conn.addr = c.Addr()
-	conn.Greeting.Version = c.Greeting().Version
+	connGreeting := c.Greeting()
+	conn.Greeting.Version = connGreeting.Version
+	conn.Greeting.Salt = connGreeting.Salt
 	conn.serverProtocolInfo = c.ProtocolInfo()
 
 	spaceAndIndexNamesSupported :=