camel-sasl-gssapi: Generate correct error messages for non-krb5 mechanisms

This code is littered with assumptions that GSSAPI means krb5. Let's fix
at least some of them, since HTTP Negotiate means SPNEGO, not just krb5.

Discussed as part of bug 732850.

[dwmw2: Some fixes and refactoring of Daniel's original patch]

(cherry picked from commit a523ac27fe9cdc8b14aeb5f6deb435f65af836f4)
camel-sasl-gssapi: Use SPNEGO for HTTP auth not bare krb5

Discussed as part of bug 732850

(cherry picked from commit bd84343424ba0ff744691ff14ec06aafe8fa1464)
Improve error on failed conversion

Not a lot of point in showing the error that we got on converting the
original error. Just show one number.

Not that this should ever happen, hopefully.

(cherry picked from commit f98caca8e677c640e170c9b8f33a57942675f918)
camel-sasl-gssapi: Always use gss_display_status() for mechanism error code

(cherry picked from commit 581c32aad09a45723d39124c51943dffac0ea9e4)
Bug 736116 - Add EBSQL_DEBUG=timing

(cherry picked from commit 67f707e9b61b460f223795b8e7505ee6da617067)