api: add helper Dialer implementations

[DerekBum]

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 check the ProtocolInfo in the created connection.
GreetingDialer is created to fill the Greeting in the created connection.

I didn't forget about (remove if it is not applicable):

• Tests (see documentation for a testing package)
• Changelog (see documentation for changelog format)
• Documentation (see documentation for documentation style guide)

Related issues:
Part of #301

[oleg-jukovec]

Thank you for the patch!

[oleg-jukovec]

Please, update the commit message: add GreetingDialer too.

[DerekBum]

Please, update the commit message: add GreetingDialer too.

It is in the commit message:

GreetingDialer is created to fill the Greeting in the created connection.

[oleg-jukovec]

Please, update the commit message: add GreetingDialer too.

It is in the commit message:

GreetingDialer is created to fill the Greeting in the created connection.

But the title is confusing. It could be something like: api: add helper Dialer implementation or something like that.

[askalt]

Thank you for the patch! lgtm

[DerekBum]

Please, update the commit message: add GreetingDialer too.

It is in the commit message:

GreetingDialer is created to fill the Greeting in the created connection.

But the title is confusing. It could be something like: api: add helper Dialer implementation or something like that.

Oh, I thought you were talking about commit body, not header. Updated commit header and PR header too.