spec file: support client-only build
    
    nspr-devel, nss-devel and openssl-devel are required for client-only build,
    move their respective BuildRequires from the server-specific BuildRequires
    section to the main BuildRequires section.
    
    Pass --enable-server or --disable-server to ./configure based on the value
    of %{ONLY_CLIENT}.
    
    Remove the `make client-check` call from %check, as the client-check target
    does not exist anymore. Always call `make check` instead.
    
    Do not package the /usr/share/ipa directory in freeipa-client-common, as it
    is not created in client-only build.
    
    https://pagure.io/freeipa/issue/6517
    
    Reviewed-By: Pavel Vomacka <pvomacka@redhat.com>