Allow skipping nvr checking for chain-build
    
    Add '--skip-nvr-check' parameter to 'chain-build command'. In fact,
    nvr checking is performed just for the last package in the chain.
    This is the package from an active repository.
    
    JIRA: RHELCMP-3013
    Resolves: rhbz#1890701
    
    Signed-off-by: Ondrej Nosek <onosek@redhat.com>