krb5_gssapi: Renamed the status variables

For consistency with the spnego code.

krb5: Moved host from Curl_auth_create_gssapi_user_message() to be argument

For consistency with the spnego and oauth2 code moved the setting of
the host name outside of the Curl_auth_cr

krb5: Moved host from Curl_auth_create_gssapi_user_message() to be argument

For consistency with the spnego and oauth2 code moved the setting of
the host name outside of the Curl_auth_create_gssapi_user_messag()
function.

This will allow us to more easily override it in the future.

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GSS: make Curl_gss_log_error more verbose

Also display the GSS_C_GSS_CODE (major code) when specified instead of
only GSS_C_MECH_CODE (minor code).

In addition, the old code was

GSS: make Curl_gss_log_error more verbose

Also display the GSS_C_GSS_CODE (major code) when specified instead of
only GSS_C_MECH_CODE (minor code).

In addition, the old code was printing a colon twice after the prefix
and also miscalculated the length of the buffer in between calls to
gss_display_status (the length of ": " was missing).

Also, gss_buffer is not guaranteed to be NULL terminated and thus need
to restrict reading by its length.

Closes #738

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vauth: Refactored function names after move to new vauth directory

Renamed all the SASL functions that moved to the new vauth directory to
include the correct module name.

vauth: Moved the Kerberos V5 authentication code to the new vauth directory