sss tools: improve option handling
    
    The crash describe by ticket #2802 is caused by providing NULL options
    in popt and yet trying to iterate over them. Instead of simply testing
    for NULL this patch creates a new option table table merges several
    option tables together, thus improving and simplifying usage string.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/2802
    
    Reviewed-by: Pavel Reichl <preichl@redhat.com>
    (cherry picked from commit bda8039465a0084fb380e878c8f9ea3e900505ea)