Add --no-dynamic-buildrequires options
    
    And set Fedora's default behavior is to enable DynamicBuildRequires.
    
    All Fedora crates use dynamic BuildRequires and are built only in
    Rawhide and is unlikely that anybody is building hundreds of crates
    outside of Fedora infrastructure.
    
    Closes: https://pagure.io/fedora-rust/rust2rpm/issue/97
    Signed-off-by: Igor Gnatenko <ignatenkobrain@fedoraproject.org>