Prior to this change tests that required NTLM feature did not require
SSL feature.

There are pending changes to cmake builds that will allow enabling NTLM
in non-SSL builds in Windows. In that case the NTLM auth strings created
are different from what is expected by the NTLM tests and they fail:

"The issue with NTLM is that previous non-SSL builds would not enable
NTLM and so the NTLM tests would be skipped."

Assisted-by: marc-groundctl@users.noreply.github.com

Ref: https://github.com/curl/curl/pull/4717#issuecomment-566218729

Closes https://github.com/curl/curl/pull/4768

RFC 4616 specifies the authzid is optional in the client authentication
message and that the server will derive the authorisation identity
(authzid) from the authentication identity (authcid) when not specified
by the client.

... and add "MAILINDEX".

As described in #2789, this is a suggested solution.  Changing UID=xx to
actually get mail with UID xx and add "MAILINDEX" to get a mail with a
special index in the mail box (old behavior).  So MAILINDEX=1 gives the
first non deleted mail in the mail box.

Fixes #2789
Closes #2815

As the email protocols implement SASL authentication rather than IMAP,
POP3 and SMTP specific authentication, updated the authentication
keywords to reflect this.