http: store credential when PKI auth is used

http: store credential when PKI auth is used

We already looked for the PKI credentials in the credential store, but
failed to approve it on success.  Meaning, the PKI certificate password
was never stored and git would request it on every connection to the
remote.  Let's complete the chain by storing the certificate password on
success.

Likewise, we also need to reject the credential when there is a failure.
Curl appears to report client-related certificate issues are reported
with the CURLE_SSL_CERTPROBLEM error.  This includes not only a bad
password, but potentially other client certificate related problems.
Since we cannot get more information from curl, we'll go ahead and
reject the credential upon receiving that error, just to be safe and
avoid caching or saving a bad password.

Signed-off-by: John Szakmeister <john@szakmeister.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>