sssctl: Flags for command initialization
    
    Allow passing flags for command specific initialization. Currently
    only one flag is available to skip the confdb initialization which is
    required to improve config-check command.
    
    Resolves:
    https://fedorahosted.org/sssd/ticket/3209
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    (cherry picked from commit cbee11e912bb391ba254b0bac8c1159c1f634533)