Modify auth get uid/gid logic to use authinfo

This change adds the AuthInfo configuration parameter to the
g_slurm_auth_get_uid() and g_slurm_auth_get_gid() functions.

Then continuing on - src/common/slurm_auth.h shows that the following
functions are intended to take the auth_info argument:
extern void *   g_slurm_auth_create( void *hosts, int timeout, char
*auth_info );
 extern int      g_slurm_auth_verify( void *cred, void *hosts, int
timeout, char *auth_info );
extern uid_t    g_slurm_auth_get_uid( void *cred, char *auth_info );
extern gid_t    g_slurm_auth_get_gid( void *cred, char *auth_info );

g_slurm_auth_create and g_slurm_auth_verify seems to be OK now - but
g_slurm_auth_get_uid and g_slurm_auth_get_gid are not (most cases will
work anyway since the munge auth plugin will only use auth_info if the
cred has not yet been verified - and in many instances it has - still
I would assume passing the information to be the safe thing to do).
I've attached two blind patches that just replaces null with
slurm_get_auth_info() for these two functions.