int getseuserbyname(const char *linuxuser, char **selinuxuser, char **level);
retrieves the SELinux username and security level associated with
a given Linux username. The SELinux username and security level can
then be passed to other libselinux functions such as
get_ordered_context_list_with_level and get_default_context_with_level.
The returned SELinux username and level should be freed by the caller
On success, 0 is returned.
On failure, -1 is returned and errno is set appropriately.
The errors documented for the stat(2) system call are also applicable